Event archive 2016

Here you can find past events of the MPSD institute and the MPSD research groups at the Universität Hamburg.

MPSD Seminar

18951 1559824357

Theoretical study on solid-state high harmonic generation: from a one-dimensional model to an ab-initio three-dimensional approach

High harmonic generation (HHG) from crystalline solids has become a playground in ultrafast phenomena. In contrast to noble gases, crystalline solids have rich physical properties, e.g. anharmonic energy dispersion, anisotropy depending on crystalline axis, strong electron-hole correlation, and so on. While the three-step model for HHG and its generalizations are successfully applicable to several situations, a deviation from the theoretical prediction is one of the most interesting physics in this field. To understand such deviations in solid-state HHG experiments, we need to go beyond the three-step model or along different directions. I will mainly talk about our recent trials to understand solid-state HHG, electron-hole attraction inclusion based on Hartree-Fock theory for 1D model crystal, and an ab-initio approach based on density-functional theory for 3D bulk solid comparing with experiments. [more]

MPSD Seminar

18967 1560253118

Electronic and Vibrational Properties of Colloidal Nanocrystals

Colloidal nanocrystals (CNCs) are nanometer sized crystals grown in solution. Due to their size-tunable optical properties, CNCs have emerged as a novel material platform for numerous applications such as displays, photovoltaics, and biological tagging. However, the colloidal growth process results in an unavoidable distribution of CNC size that inhomogeneously broadens optical absorption/luminescence lineshapes. 2-D spectroscopy is a technique capable of circumventing inhomogeneous broadening by correlating absorption and emission dynamics. In this talk I will present our results from applying 2-D spectroscopy to CNCs at cryogenic temperatures. I will first discuss our experiments on conventional CdSe CNCs, in which we have simultaneously observed both bulk-like acoustic phonons and acoustic vibrations discretized by the nanocrystal geometry for the first time. Next, I discuss our experiments on perovskite CNCs, which are a new class of materials first synthesized in 2015. We demonstrate that coherences due to vibrational coupling exhibit anomalous dephasing dynamics, which we attribute to a cascaded coherence transfer process. Finally, I discuss our observations of coherences between so-called bright-triplet exciton states, which are robust at high temperatures and polarization-selective. [more]

MPSD Seminar

18952 1559824853

Correlated driven-dissipative systems

Driven-dissipative systems represent natural platforms to study non-equilibrium phases. In the first part of the talk, I will present some physical results for which both non-equilibrium conditions and interactions are crucial. I will argue that a prototype model of correlated driven-dissipative lattice bosons, relevant for upcoming generation of circuit QED arrays experiments, exhibits a phase transition where a finite frequency mode becomes unstable, as an effect of quantum interactions and non-equilibrium conditions. In the broken-symmetry phase the corresponding macroscopic order parameter becomes non-stationary and oscillates in time without damping, thus breaking continuous time-translational symmetry. To get some more insights on this transition, I studied the spectral properties of Markovian driven-dissipative quantum systems using a Lehmann representation. Focusing on the nonlinear quantum Van der Pol oscillator as a paradigmatic example, I showed that a sign constraint of spectral functions, which is mathematically exact for closed systems, gets relaxed for open systems; it is eventually replaced by an interplay between dissipation and interactions. In the last part of the talk, I will finally discuss a new method to solve quantum impurity models, small interacting quantum systems coupled to a non-Markovian environment, in presence of additional Markovian dissipation. I will derive a Dyson equation for the time-evolution operator of the reduced density matrix and approximate its self-energy resuming only non-crossing diagrams. I will test this approach on a simple problem of a fermionic impurity. [more]

MPSD Seminar

18927 1559648179

Tuning quantum materials out of equilibrium: A FIB-microstructuring approach

“Quantum materials” loosely defines a broad collection of materials whose ground states are defined by unusual quantum properties. This research largely focuses on macroscopic single crystals, yet naturally interesting quantum phenomena lie beyond their equilibrium state. My group works towards reducing the sample size onto the sub-mm length scale, following the general idea that small samples can be driven more strongly and react faster than on the macro scale. Our main tool is Focused Ion Beam machining capable of cutting single crystals into high quality quantum devices. I will present two concrete research projects showcasing how new quantum states out of equilibrium can be accessed and investigated in FIB-prepared microcrystal structures. The first concerns the heavy fermion superconductor, CeIrIn5 (Tc~400mK). When a mm-sized structure is firmly coupled to a mm-sized substrate of different thermal expansion, the microstructure is under significant strain at low temperatures. By precisely controlling its shape, the emergent strain field can be controlled. The key difference to other approaches, such as uniaxial strain, is that complex, yet well-controlled, spatially varying strain fields can be achieved. In collaboration with Katja Nowack (Cornell), we have experimentally mapped out the resulting superconducting landscape in the devices using scanning-SQUID microscopy, and show that this spatial modulation can be well captured by finite element simulations. [1] Second, I will present our ongoing efforts to experimentally identify pseudo-magnetic fields in 3D Dirac semi-metals [2,3]. Owing to their Dirac dispersion, deformation of the crystal structure does not open a gap at the nodes, but shifts the location of the nodes in k-space and hence playing the role of a “pseudo-magnetic field”, B5. I will show how microstructuring gives us unprecedented control of such a process, and discuss how future. [more]

MPSD Seminar

18880 1559038731

Electrical control of quantum spins

Magnetic fields are challenging to localise to short length scales because their sources are electrical currents. Conversely, electric fields can be applied using electrostatic gates on scales limited only by lithography. This has important consequences for the design of spin-based information technologies: while the Zeeman interaction with a magnetic field provides a convenient tool for manipulating spins, it is difficult to achieve local control of individual spins on the length scale anticipated for useful quantum technologies. This motivates the study of electric field control of spin Hamiltonians [1]. Mn2+ defects in ZnO exhibit extremely long spin coherence times and a small axial zero-field splitting. Their environment is inversion-symmetry-broken, and the zero-field splitting shows a linear dependence on an externally-applied electric field. This control over the spin Hamiltonian offers a route to controlling the phase of superpositions of spin states using d.c. electric field pulses, and to driving spin transitions using microwave electric fields [2]. Experiments on Mn defects in ZnO provide insights into how to achieve manipulation of individual spins on surfaces using a scanning tunnelling microscope. A high-frequency voltage applied to the tip can drive electron spin resonance in Fe atoms on MgO surfaces via modulation of the crystal field experienced by the Fe atom [3]. It has been proposed theoretically that frustrated exchange-coupled molecular clusters might offer sensitivity to externally-applied electric fields [4]. Experiments on an antiferromagnetically-coupled Cu3 compound reveal a small linear electric field effect. A comparable sensitivity is exhibited by the heterometallic S = 1 antiferromagnetic ring Cr7Mn, but no effect is found for the S = 1/2 Cr7Ni [5]. [more]

MPSD Seminar

18727 1558002303

Fractional Excitonic Insulator

We argue that a correlated fluid of electrons and holes can exhibit a fractional quantum Hall effect at zero magnetic field analogous to the Laughlin state at filling 1/m. We introduce a variant of the Laughlin wavefunction for electrons and holes and show that for m=1 it describes a Chern insulator that is the exact ground state of a free fermion model with p_x + i p_y excitonic pairing. [more]

Reimar Lüst Lecture

17974 1556545060

Reimar Lüst Lecture -Prof. Charles Kane: Symmetry, topology and electronic phases of matter

Symmetry and topology are two of the conceptual pillars that underlie our understanding of matter. While both ideas are old, over the past several years a new appreciation of their interplay has led to dramatic progress in our understanding of topological electronic phases. A paradigm that has emerged is that insulating electronic states with an energy gap fall into distinct topological classes. [more]

MPSD Seminar

18814 1558428743

Unconventional Charge Density Wave Transitions

Historically charge density waves have been associated with the notions of Fermi surface nesting and, at the transition temperature, a soft phonon mode. In this talk, I will present two cases that defy this common theme. First, I will show that TiSe2 undergoes a transition due to exciton condensation, which exhibits a soft mode of a different, electronic variety. Second, when driving the system away from equilibrium, the phase transition is mediated by topological defects. These defects allow for the formation of a charge density wave that does not occur in equilibrium. This light-induced charge density wave shows some unique properties that suggest that it is not just a trivial extension of an equilibrium one. [more]

MPSD Seminar

18710 1558002578

Engineering with vacuum fields

When a collection of electronic excitations are strongly coupled to a single mode cavity, mixed light-matter excitations called polaritons are created. The situation is especiallyinteresting when the strength of the light-matter coupling Ωr is such that the coupling energy becomes close to the one of the bare matter resonance ω0. For this value of parameters, the system enters the so-called ultra-strong coupling regime, in which a number of very interesting physical effects were predicted. Using metamaterial coupled to two-dimensional electron gases[1], we have demonstrated that a ratio Ωr/ω0 close to[2] or above unity can be reached. [more]

MPSD Seminar

18709 1558002599

Ab initio few-mode theories for quantum potential scattering problems

The concept of a single mode of the electromagnetic field interacting with matter has been a paradigm in the field of light-matter interactions. For example, the single mode Jaynes-Cummings model and its many generalizations have been indispensable tools in studying the quantum dynamics of various systems. In particular in cavity and circuit QED, where strong light-matter coupling is routinely achieved in experiment, such models have been tremendously successful [1]. [more]

IMPRS-UFAST core course

17964 1551966351

Solid State Physics

From a microscopic point of view, a solid is just a regular arrangement of atoms, embedded in a soup of electrons. Yet, a remarkably rich manifold of phenomena emerges from this simple starting point, ranging from simple metals and semiconductors to multiple kinds of magnetic order or superconductivity. In this course we will discuss basic properties of solids and their microscopic understanding.Topics include:- band theory- screening- phonons - ordered phases [more]

MPSD Seminar

18197 1554453272

Shedding New Light on Dirac Materials with Nonlinear Optics

Nonlinear optics has recently emerged as an attractive approach for both probing topological properties and driving Dirac materials into new states. Here, I will describe our use of ultrafast nonlinear optics to study three representative Dirac materials: graphene micro-ribbons, topological insulators, and Weyl semimetals. [more]

MPSD Seminar

18171 1553782985

Quantum enhanced super-resolution microscopy

Although the principles of quantum optics have yielded multiple ideas to surpass the classical limitations in optical microscopy, their application in life science imaging has remained extremely challenging. In this talk, I will present two works that apply measurements of photon correlations for the benefit of localization microscopy and image scanning microscopy (ISM). The first uses photon antibunching measurement to estimate the number of emitters in a fluctuating scene and can potentially speed-up super-resolution techniques based on localization microscopy [1]. In the second work, we employ photon antibunching as the imaging contrast itself. Measuring the spatial distribution of ‘missing’ photon pairs in an ISM architecture may enhance lateral resolution four time beyond the diffraction limit [2]. The robustness of the antibunching signal enabled super-resolved imaging of fixed cells, relying solely on a quantum contrast. [more]

MPSD Seminar

18182 1553856301

Many-body dynamics in pump and probe experiments: From light amplification to terahertz STM

I will discuss new theoretical approaches for analyzing pump and probe experiments in solid state systems. The focus will be on combining theoretical techniques from condensed matter physics and quantum optics. Several examples will be discussed, including light amplification in photo-excited superconductors and insulators, ultrafast molecular dynamics in terahertz-STM experiments. [more]

MPSD Seminar

18169 1553782920

Non-equilibrium control of the effective free energy landscape in a frustrated magnet

Geometrically frustrated magnets often possess accidentally degenerate ground states at zero temperature. At low temperature, thermal fluctuations lift the accidental degeneracy and tend to stabilize ground states with maximal entropy. This phenomenon, known as “order by disorder”, underlines the fluctuation contribution to the free energy landscape in frustrated magnets.In this talk, I show that one can control such free energy landscape in a non-equilibrium setting. In a frustrated magnet with precessional dynamics, the system’s slow drift motion within the degenerate ground state manifold is governed by the fast modes out of the manifold. Exciting these fast modes generates a tuneable effective free energy landscape with minima located at thermodynamically unstable portions of the ground state manifold. I demonstrate this phenomenon on pyrochlore XY antiferromagnet, where a magnetic field pulse is sufficient for controlling the effective free energy landscape at nonequilibrium. [more]

MPSD Seminar

17985 1553598600

Ab-initio description for propagation of extreme light pulse in solids: recent progresses

When we theoretically investigate interaction of an intense and ultrashort laser pulse with solids, there are two aspects that should be considered: the strong electric field of the light pulse induces nonlinear electron dynamics in solids, and the nonlinear polarization that arises from the electron dynamics affects the propagation of the light pulse. [more]

MPSD Seminar

17971 1553598659

Coherent states of light and ordered states of matter in cavity QED

Collective phenomena originating from interactions between light and matter have become a major focus of interest spanning different fields of research. [more]

MPSD Seminar

18035 1552472824

Cooperative valence dynamics in Anderson Lattices observed by resonant inelastic x-ray scattering

In rare earth intermetallics with weakly bound f-electrons and a Kondo energy scale much larger than magnetic exchange interactions or crystal field splittings, the screening of local moments may result in a non-magnetic Fermi liquid ground state [1]. At low temperatures, the quantum fluctuations between magnetic and non-magnetic valence configurations can then acquire a cooperative (lattice) character. On a phenomenological basis, a sound understanding of this Anderson Lattice phenomenon has been achieved. On the other hand, the microscopic description of the coherent coupling between Kondo-screened sites remains an outstanding theoretical challenge [2]. In experiment, the cooperative character of Anderson Lattices has only recently become directly accessible. Momentum-resolved spectroscopies, such as angle-resolved photoemission and inelastic neutron scattering, reveal the emergence of characteristic low-energy quasiparticle dynamics at low temperatures [3]. These methods probe single-particle excitations in the charge and magnetic channels, respectively. By contrast, high-resolution resonant inelastic x-ray scattering (RIXS) experiments couple to both charge and spin degrees of freedom in a non-trivial way and thus provide a more subtle point of view. If calculations of the underlying Kramers-Heisenberg term on a basis of strongly correlated f-electronic bands are achieved, RIXS may unlock unprecedented microscopic insights into the entanglement of local and itinerant charge and magnetic degrees of freedom. This would address a fundamental mechanism of quantum matter, with relevance far beyond lanthanides and actinides. I will review previous spectroscopic investigations of intermediate valence materials, present our recent RIXS results on the archetypal Anderson Lattice compound CePd3, and highlight some ideas for future x-ray scattering studies at 3rd and 4th generation light sources. [more]

MPSD Seminar

18034 1552472212

Single-shot optical probing of laser-generated plasmas

Lasers have captured scientific interest since their inception and increase in the on-target intensity has resulted in powerful petawatt (≈1015W) laser systems across the globe [1]. Such a laser gives the possibility to study and optimize processes such as electron [2] or ion [3] acceleration resulting from interaction of extreme electric fields (E ≥ 0.5 TV/m) with matter 0. In this talk, I would outline the current efforts of POLARIS (a Petawatt laser system) in Jena to study the effects of such laser-plasma interaction. A single-shot all optical probing was performed with Aluminum targets to fully characterize the plasma evolution. The basic motivation of the work, the experimental setup used and some results would be presented in the talk. [more]

MPSD Seminar

17647 1549554641

Manipulating quantum materials with cavity fields

We investigate ground state properties of electronic materials strongly coupled to cavity fields. In a two-dimensional electron gas, we explore electron paring mediated by vacuum fluctuations of the transverse electromagnetic field. To date, these interactions have only been discussed in free space, where their impact is restricted to extremely low temperatures. We argue that the sub-wavelength confinement of the light field in nanoplasmonic cavities can enhance the induced interaction to an experimentally accessible regime. In a one-dimensional Hubbard model, the cavity further enhances magnetic couplings at half-filling, and introduces next-nearest-neighbor hopping. References: F. Schlawin, A. Cavalleri, and D. Jaksch, arXiv:1804.07142. M. Kiffner, J. Coulthard, F. Schlawin, A. Ardavan and D. Jaksch, arXiv: 1806.06752. [more]

MPSD Seminar

17608 1549376870

Nonequilibrium dynamics in strongly correlated systems: spin-charge coupling in a photodoped Mott insulator and possible induced superconductivity

Nonequilibrium pump-probe time-domain spectroscopy opens new perspectives in studying the dynamical properties of the strongly correlated electron systems. In particular, the interplay between different degrees of freedom in strongly correlated materials can be studied by their temporal evolution [1] and also the optical switching to some novel phases is possible [2]. [more]

MPSD Seminar

17490 1548337981

Strain, lattice distortions and the metal-insulator transition in correlated electron materials

Correlation-driven metal-insulator transitions are typically coupled strongly both to local (octahedral distortion) and long wavelength (strain) lattice distortions. I present a theory of the intertwined electronic and lattice transitions in correlated materials, and show how it accounts for phenomena ranging from the interplay between nematic and magnetic ordering in pnictide superconductors, to the strain and current dependence of the metal insulator transitions in Ca2RuO4 and Ca3Ru2O7 and superlattice effects in the rare earth nickelates. [more]

MPSD Seminar

17056 1545215883

Probing Topological Matter by «Heating»: From Quantized Circular Dichroism to Tensor Monopoles

The intimate connection between topology and quantum physics has been widely explored in high-energy and solid-state physics, revealing a plethora of remarkable physical phenomena over the years. Building on their universal nature, topological properties are currently studied in an even broader context, ranging from ultracold atomic gases to photonics, where distinct observables and probes offer a novel view on topological quantum matter. [more]

MPSD Seminar

16937 1544611408

Charge density wave (CDW) order in monolayer TMDs

Charge density wave (CDW) ordering and the mechanism for it remains a live issue, particularly in transition-metal dichalcogenide (TMD) systems. These are attractive because of both the variety of material properties they are known to host, and their conveniently layered van der Waals structures. The evolution of properties and interactions of these materials when thinned to a monolayer limit remains an area for exploration. In this talk, I present some background on the study of CDW order in bulk and monolayer TMDs. I then discuss some recent results, as well as my own upcoming investigations of TiTe2, utilising molecular beam epitaxy (MBE) growth and photon energy-dependent angle resolved photoemission spectroscopy (ARPES). [more]

MPSD Seminar

16995 1544449761

Probing (and Changing) the Mechanical Properties of Cell Membranes

Cell membranes are formed of lipid bilayers, and separate the interiors of all living cells from the surroundings. They have an integral role in maintaining the internal environment of cells. Anaesthetics have been shown to have a potency directly proportional to their affinity for lipid substances, strongly implying that the effect of anaesthesia is due to the action on cell membranes of the anaesthetic molecules. Previous studies have demonstrated the effects of anaesthetics on lipid melting points, but no experiments have looked at changes in mechanical properties. [more]

IMPRS-UFAST core course: Non-linear optics

16194 1542709013

Non-linear optics

Nonlinear optics (NLO) is one of the most fascinating fields of modern physics. It deals with light-matter interactions at extreme electro-magnetic field strengths. Such fields are today routinely available thanks to laser technology. NLO started with the observation of second harmonic generation from a ruby laser in 1961, just 1 year after the first laser was operated. It allows producing optical pulses with durations in the femtosecond (fs, 10-15 s) and even attosecond (as, 10-18 s) order. With such sources, one can observe chemical reactions, physical and biological phenomena in real time. During the lectures, I will give a short overview of NLO. I will discuss the main physical phenomena (second harmonic generation, optical parametric amplification, difference and sum frequency generation, white light generation, third harmonic generation, high harmonic generation…) and some of their applications, and conclude with the newest trends of research like coherent pulse synthesis. [more]

MPSD Seminar

16884 1543579363

A time domain perspective on electron-boson coupling in superconducting materials

Experiments in the time domain allow to determine the electron-boson coupling strength by analyzing the second moment of the Eliashberg function α2∙F(ω) using the relaxation time constant of thermalized, hot electrons after optical excitation. [1] While this approach works well for conventional superconducting materials, it is under discussion for unconventional superconductors due to competing electron and boson dynamics on similar time scales. [2,3] [more]

MPSD Seminar

16936 1543930707

New Methods of Measuring Material Structure Using X-Ray Diffraction Data

In this talk I will discuss how the classical theory of x-ray diffraction can be used to simulate the intensity pattern produced by a powdered sample, generalised to the case where the finite size of the crystallites in the sample is accounted for. I will then explain how we are using this theory to develop new methods of measuring the shape and size of crystallites in a fractured crystal sample from x-ray diffraction data. [more]

MPSD Seminar

16665 1543492206

Nano Surface Science and Engineering for Energy Conversion and Diamond Transistors

Nano science and technology offer a vast and fascinating playground
to explore the novel physiochemical properties of nanomaterials with the development for various applications including energy conversion and electronics. [more]

MPSD Seminar

16745 1543402156

Ultrafast dynamics in condensed matter: from 2D materials to molecular magnets

The key to designing modern optoelectronic and magnetic functional materials lies in understanding how the charge carriers respond to the excitation on ultrafast timescales – tens or hundreds of femtoseconds. In this talk, I will introduce two projects which attempt to shed light on the fundamental processes behind the remarkable physics of two-dimensional materials and molecular magnets, and how we can control them. [more]

IMPRS-UFAST focus course

15106 1542708944

Hubbard Model

The Hubbard model is the drosophila of condensed matter physics. It is perhaps the simplest possible model capturing the competition between localization of electrons in solids due to Coulomb repulsion and delocalization in energy bands due to kinetic energy lowering. Invented in the early 1960s to descibe magnetism in transition-metal monoxides, it has been generalized and applied to a host of problems in condensed matter including heavy fermions or high-temperature superconductors. Despite its apparent simplicity it shows complicated phase diagrams that depend on dimensionality and lattice coordination as well as electronic filling, with only few exact solutions in limiting cases known to this date. [more]

MPSD Seminar

16198 1542719197

An introduction to coupled-cluster theory, and recent developments in quantum embedding

Coupled-cluster theory has become a key tool in quantum chemistry, providing gold-standard accuracy for ground- and excited-state energetics, and other properties. [more]

MPSD Health Seminar

16054 1541756573

1st MPSD HEALTH DAY

Invitation to the 1st MPSD HEALTH DAY [more]

MPSD Seminar

16108 1542207560

Ultrafast control of matter by high-field terahertz pulses

Terahertz interaction with matter has become one of the hottest topics in ultrafast community. Indeed, intense terahertz pulses have recently proved to be a pivotal tool to manipulate and control the properties of materials and especially complex condensed matter systems. The recent development of terahertz sources driven by lasers and accelerators has led to pioneering experiments demonstrating the access to new metastable phases of matter and nonlinear processes hindered to conventional laser excitation.In this talk, I will give an overview on the high-field terahertz generation and present the capabilities of the nonlinear terahertz spectroscopy. Recent experiments, including terahertz driven insulator-to-metal transition, nonlinear optical processes and coherent phonon control, are discussed. [more]

IMPRS-UFAST focus course

15128 1540562286

Photoinduced Energy and Electron Transfer in the Natural and Artificial Systems

One of the most active areas of research is to assemble rationally tailored components at molecular level, which can capture the sunlight energy and transfer it in the desired directions. Biological protein systems, such as the antenna complexes, transfer the absorbed solar energy with unit efficiency into the reaction center, where the charge separation directs the water splitting. This course will provide an introduction to the processes of energy and electron transfer with the help of examples from natural photosynthetic complexes and organic photovoltaics. [more]

IMPRS-UFAST core course

15934 1540562225

Basics of chemistry and biochemistry - IMPRS-UFAST core course

  • Start: Nov 6, 2018 10:00
  • End: Nov 15, 2018 13:30
  • Speaker: Melanie Schnell, Marta San Valls and Sam Horrell
  • In this course, chemistry will mainly be understood as reactions. The course gives an overview about the basics of reaction chemistry and discuss what is already known and what can be measured in the laboratory nowadays (i.e. describing the current frontiers and where the research performed at CFEL can make a difference). In the biochemistry part, the basic principles of nucleic acids (DNA, RNA, their replication etc.) and proteins, their structure and function etc. will be discussed. It will be interesting to work out where the new coherent sources can advance the field.
  • Location: CFEL (Bldg. 99)
  • Room: Seminar Room O1.060
  • Host: IMPRS-UFAST

[more]

MPSD Seminar

15877 1540388639

DIALS for ED: Adapting X-ray software for electron diffraction integration

In recent years, electron diffraction has arisen as an alternative to X-ray diffraction for structural studies on threedimensional crystals. Promising features of the technique include complete data sets from a few or even singlenanocrystals, sensitivity to the charged state of ions and the relatively low expense of the apparatus. Experimentalprotocols and detector technologies are improving, so that data collection using the rotation method, dominant inX-ray crystallography, is now feasible in a cryoTEM. This convergence of experimental techniques has beenaccompanied by repurposing of analysis tools: robust and sophisticated algorithms developed over decades forX-ray diffraction integration software can be now employed to tackle electron diffraction data. Nevertheless, thegeometry of the electron diffraction experiment incurs specific challenges to address in the analysis. Here, thediffraction integration package DIALS is discussed, highlighting particular adaptations that were made to thesoftware for various example cases of electron diffraction, particularly on protein crystals. The experience gainedindicates that integration of good quality ED data can be straightforward, but the bottleneck remains with collectionof such good data, which relies on careful calibration and understanding of the instrument. Improved apparatus willameliorate this issue and future studies to develop improved models for details including dynamic diffraction andabsorption are anticipated. [more]

MPSD Health Seminar

15694 1539066993

Resilience: scientific background and its implications for our every-day life

Resilience and burnout both are not well defined concepts. But whereas theories about the development of a burnout-syndrom stress pathological pathways, theories about resilience are based on the concept of salutogenesis: two sides of thesame coin? [more]

MPSD Seminar

15808 1539873705

Exploring and Exploiting Photoacids to Reveal Ultrafast Hydrogen Bond and Proton Transfer Dynamics in Solution: How to Move from the Mid-IR to the Soft-X-Ray Regime

Elementary steps of proton transfer between acids and bases occur on ultrafast time scales. To elucidate the microscopic mechanisms of proton transfer many research groups have applied time-resolved spectroscopy utilizing a class of organic molecules called photoacids. In this talk I will provide an overview of results obtained by my research team on photoacid molecules with ultrafast infrared spectroscopy as a local probing technique. Whereas profound insight in aqueous proton transfer pathways in acid-base neutralization have been achieved in recent years, the underlying reasons for photoacidity have remained unsolved. Recent developments will be discussed how to tackle this unsolved question using the technique of soft-x-ray spectroscopy as an alternative local probe. For this liquid flatjet technology appears to be a highly promisingmethodological approach. [more]

MPSD Seminar

15742 1539615484

Elisa Palacino Gonzalez - Molecular Photodynamics of Open Quantum Systems. Simulation of Nonlinear Optical Spectroscopies using Nonperturbative Approaches

The theoretical description of nonlinear optical spectroscopy has traditionally been laid in the framework of perturbation theory. Within this formalism, an intuitive approach to the understanding of the dynamics of a molecular system excited by several external laser pulses is based on the concept of nonlinear response functions. However, as the system complexity increases or nontrivial dynamic effects have to be taken into account (nonadiabatic interstate couplings, bath-induced relaxation) the perturbative approach becomes computationally expensive. To tackle this scenario nonperturbative approaches based on the numerically exact solution of quantum equations of motions have been developed. [more]

MPSD Seminar

15553 1538124042

In Celebration of Basic Science: From the First Atomic Movies of Strongly Driven Phase Transitions to Star Trek Surgery

The 2018 European Physical Society Award Lecture for Research in Laser Science and Applications: The Picosecond Infrared Laser (PIRL) Scalpel: Achieving Fundamental (Single Cell) Limits to Minimally Invasive Surgery and Biodiagnostics. Followed by: The Future of PIRL Technology: Presentations and Round Table Discussion [more]

MPSD Seminar

15741 1539608230

Michael Bonitz - Femtosecond electron dynamics in strongly correlated finite systems

[more]

IMPRS-UFAST focus course

14863 1533126882

Brief overview of Quantum Dissipative Systems: techniques and applications

This course covers an operational introduction to the dissipative quantum systems. Starting with a descriptive introduction we will introduce four essential techniques: I.Liouville Equation II.Generalized Master Equation III.Lindblad Equation and IV.Equations of motion approach, each of them will be illustrated with the help of following examples: driven quantum dot/ phonon which is an essential prototype for condensed matter systems and Jaynes Cummings model borrowed from quantum optics literature. Measurable observables relevant to experiments will be discussed. [more]

MPSD Seminar

15344 1536838877

Experimental study of carbon nanotube resonator

In recent years, due to the maturity of micro-nano fabrication technology, artificial nano-structures are widely studied, people actively explore the mechanical, thermal, optical and electromagnetic properties in a variety of nano-materials, among which the nano-mechanical resonator draws great attention for its potential use to study the light-matter interactions. In this presentation, I will first report our experimental results of two carbon nanotube mechanical resonators that are strongly coupled when the frequencies of them are tuned very close to each other. The vibrations of the two resonators superpose to produce a frequency splitting phenomenon, indicating a strong coupling regime. Second, a parametric strong coupling between two different modes within single mechanical resonator in linear regime of small amplitudes will be presented, which is different from the strong modes coupling in nonlinear regime. Finally, I will show that a back-and-forth coherent exchange of phonon energy in two different vibration modes, to realize a classical Rabi oscillations. [more]

MPSD Seminar

15343 1536838669

Study of pressure-induced abnormal ice growth and multipath water-ice transition with dynamic diamond anvil cell

Water, due to its unique hydrogen bonds, is one of the materials exhibiting diverse phases, crystal morphologies, and phase transformation. As a result of interplay between environmental conditions and molecular kinetics, more than 25 crystalline and amorphous ices have been reported with various growing morphologies from polyhedron to needle. Dynamic diamond anvil cell (dDAC), which may simply resolve the interference of macroscopic driving force and microscopic kinetics by changing compression rate, is essential to study complex phase transition behaviour of water. In the present study, we haveinvestigated the effect of compression rate on crystal growth and the multiple freezing-melting pathways of H2O under far-from-equilibrium condition by using dDAC at room temperature. First, we reveal the origin of shock growth of ice VI single crystal. Under rapid compression (strain rate > ~0.1 /s), we observed a morphological transition in ice VI growth from three-dimension (3-d) to twodimension (2-d) with one-order higher growth speed. It is found that local growth condition and interface kinetics can be affected by compression rate, which facilitate the 2-d shock growth. Secondly, we explore five different pathways of freezing and melting of deeply supercompressed water and ice via metastable phases. We will discuss the mechanism of freezing and melting by calculating driving force and interfacial free energy based on the classical nucleation theory, and comparing structure of supercompressed water and stable and metastable ices obtained from Raman spectroscopy. [more]

MPSD Seminar

15167 1536071247

Strain tuning of quantum materials

In this talk I will discuss the development of novel methods of applying uniaxialpressure to single crystals of quantum materials. Much of our work so far hasbeen on ruthenates, but I will also mention projects on other materials. I willshow that it is now possible to strain single crystals, reversibly, to change latticeparameters by at least 1%, and that this provides a ‘tuning energy scale’equivalent to the Zeeman energy of magnetic fields of well over 1000T. Uniaxial techniques are particularly suited to controlled tuning throughLifshitz transitions, and are also a useful complement to epitaxial strain in thenfilms, which is usually biaxial. [more]

MPSD Seminar

15168 1536071358

California New Age Physics: Sunshine, Crystals, and Quantum Geometry of Bands

Nonlinear optical properties of materials are important as tools in basicresearch and optical technology. Recently there has been a tremendousupsurge of interest in optical nonlinear effects, especially in crystals with curvedbandstructure geometry. Such materials are candidates for applications basedon the conversion of light to dc current. In this talk I describe our discovery thata family of Weyl semimetals has by far the largest second-order susceptibility ofany previously known crystal. In puzzling over this result, we uncovered asurprising theorem relating the strength of optical nonlinearity to a quantuminvariant property of the bandstructure that unites nonlinear optics with thecelebrated “modern theory of polarization.” This quantum invariant provides anew strategy for algorithmic computational searches for nonlinear materialswith optimal response functions. [more]

MPSD Seminar

15241 1536680558

Ultrafast quasiparticle dynamics and electronphononcoupling in single-layer FeSe/SrTiO3 and(Li0.84Fe0.16)OHFe0.98Se

Distinctive superconducting behaviors between bulk and monolayer FeSe make it challenging to obtain a unified picture of all FeSe-based superconductors. Here, we investigate the ultrafast quasiparticle dynamics of an intercalated superconductor (Li1-xFex)OHFe1-ySe, which is a bulk crystal but shares a similar electronic structure with single-layer FeSe on SrTiO3. We obtain the electronphonon coupling (EPC) constant λ (0.24 ± 0.03), which well bridges that of bulk FeSe crystal and single-layer FeSe/SrTiO3 [1]. Moreover, we find that such a positive correlation between λ and superconducting Tc holds among all knownFeSe-based superconductors, even in line with reported FeAs-based superconductors. Our observation indicates possible universal role of EPC in the superconductivity of all known categories of iron-based superconductors, which is a critical step towards achieving a unified superconducting mechanism for all iron-based superconductors.References:[1] Y. C. Tian, W. H. Zhang, F. S. Li, Y. L. Wu, Q. Wu, F. Sun, G. Y. Zhou, L. L. Wang, X. C. Ma, Q. K. Xue, Jimin Zhao, Ultrafast dynamics evidence of high temperature superconductivity in single unit cell FeSe on SrTiO3. PRL 116, 107001 (2016). [more]

MPSD Seminar

14806 1532601153

Ultrafast Laser-induced Kinetics in Two-dimensional Crystals

I will talk about our findings on the theory of ultrafast and ultrastrong optical field interacting with two-dimensional materials with an emphasis on honeycomb-shaped structures such as graphene. In fact, this talk is the emergence of two important and growing branches of science: ultrafast optics and 2D nanocrystals. Ultrafast optics or more specifically, attosecond science, is developed to study the quantum mechanical dynamics of electrons, both collective and individual, on atomic and molecular scales and in high-density mesoscopic systems. Recent advances in attosecond metrology and generation of ultrashort optical pulses with just a few oscillations of the electric field have provided real-time access to the motion of electrons on atomic and sub-atomic scales and opened a unique possibility for the coherent control of electron dynamics at sub-femtosecond time scale. Hence, the research and exploration of ultrafast dynamics of electrons in novel graphene-like materials under the illumination of few-cycle optical fields should prove useful to a growing community of scientists and hold promises for the future technologies especially high-speed memories, ultrafast imaging, and petahertz signal processing. [more]

MPSD Seminar

14352 1528971755

Higgs modes in d-wave and multi-band superconductors

Higgs mode (collective amplitude mode) in superconductors, recently detected and analysed in a conventional, s-wave superconductor, opens a novel avenue for probing the U(1) symmetry broken state. Now we have extended the notion to an unconventional, d-wave high-Tc cuprate, where a characteristic third-harmonic generation hallmarks the d-wave superconductor in a space-group resolved manner[1]. We can also predict unique features in Higgs and Leggett (phase) modes if we turn to multiband superconductors[2].[1] K. Katsumi et al, PRL 120, 117001 (2018).[2] Y. Murotani et al, PRB 95, 104503 (2017). [more]

MPSD Seminar

14351 1528971526

Superconductivity in single- and multi-band Hubbard models: can we optimise them?

We can capture various unconventional high-Tc superconductors basically either with single-band models or multiband ones. We can theoretically explore how we can optimise them for higher Tc's. There, "multiband" should not be confused with "multiorbital" systems, for which I shall compare merits and demerits of the two classes from both quantum many-body algorithms and materials-science points of view. For the former, I shall mention the dynamical vertex approximation to fathom the correlation between the electronic structure and the superconductivity and to search for enhanced Tc's. For the latter, I shall present various ideas that include "flat-band" superconductivity. [more]

MPSD Seminar

14402 1529494756

Ultrafast pump-probe spectroscopy in the ultra violet wavelength region

Explanation of the Pump-Probe spectroscopic technique with ultrashort pulses in the ultra-violet region.Firstly, it reveals the two fundamental requirements for our experiments, which are the generation of sub-20 fs monochromatic pulses, the pump pulses, in the UV and the generation of a second broadband pulse, the probe, explaining in detail the method that we used to overcome issues and problems. Experimental setup and components are described carefully, focusing on the physics principles behind. Then some experimental data are shown for Triptophan and Azzurin, in order to try to better understand the fast processes which happen in organic molecules. [more]

MPSD Seminar

14350 1528971302

Higgs mode in the d-wave cuprate superconductor Bi2Sr2CaCu2O8+δ induced by an intense THz pulse

The nonequilibrium dynamicis of the superconductors has been intensively studied over decades. Among the viriety of nonequlibrium phenomena, the study of the collective dynamics of superconducting order parameter is of essential importance, as it provides deep insights into the properties of the order parameter. Recent developments of generating intense electromagnetic pulses in the terahertz (THz) frequency range have enabled the access to low energy collective modes without giving excess energy to the system. Particularly the amplitude fluctuation of the order parameter, referred to as the Higgs mode, has been observed in a conventional s-wave superconductor Nb1-xTixN [1,2]. Its extension to unconventional d-wave superconductors is intriguing, whereas it has been nontrivial whether the Higgs mode in d-wave superconductors is observable or not. [more]

MPSD Seminar

14320 1528463795

Quantum Nanoscience: Atoms on Surfaces

The scanning tunneling microscope is an amazing tool because of its atomic-scale spatial resolution. This can be combined with the use of low temperatures, culminating in precise atom manipulation and spectroscopy with microvolt energy resolution. In this talk we will apply these techniques to the investigation of the quantum spin properties of magnetic atoms sitting on thin insulating films. [more]

MPSD Seminar

14290 1528280544

Workshop on Open Access Publishing

How can you publish via Open Access journals and boost your citations? What are GOLD and GREEN Open Access? Which science journals have Open Access or reduced fee agreements with the Max Planck Society? These and many other questions will be answered at this two-hour workshop. Open to all. To register, please mail jenny.witt@mpsd.mpg.de. [more]

MPSD Seminar

14164 1526650434

Gapless excitations in the ground state of 1T-TaS2

1T-TaS2 is a layered transition metal dichalcogenide with a very rich phase diagram, which was investigated since the early 1970s. At T=180K it undergoes a metal to Mott insulator transition. Mott insulators usually display anti-ferromagnetic ordering in the insulating phase but 1T-TaS2 was never shown to order magnetically. We have shown that 1T-TaS2 has a large paramagnetic contribution to the magnetic susceptibility but it does not show any sign of magnetic ordering or freezing down to 20mK, as probed by muSR, possibly indicating a quantum spin liquid ground state. Although 1T-TaS2 exhibits a strong resistive behavior both in and out of plane at low temperatures we find a linear term in the heat capacity suggesting the existence of a Fermi-surface, which has an anomalously strong magnetic field dependence. [more]

MPSD Seminar

14278 1528202927

Quantum control and dynamics with x-rays

More than fifty years ago, it was the invention of the laser that revolutionized atomic physics and laid the foundations for quantum optics and coherent control. With only optical frequencies available, the interaction of coherent light with matter was for a long time mainly restricted to atomic transitions. Only recently have novelhigh-frequency light sources rendered x-ray quantum optics possible. In this higher frequency regime, atomic nuclei rise as natural candidates for the interaction with coherent light creating a new bridge between atomic physics, quantum optics and nuclear condensed matter physics. Nuclei are very clean quantum systems, well isolated from the environment and benefiting from long coherence times. Combining the advantages of x-rays and nuclei, a prominent incentive is to exploit x-rays as the future quantum information carriers or for novel probing technologies based on quantum effects. Furthermore, the control of nuclear transitions would open the possibility to use long-lived nuclear excited states as a compact and clean energy storage solution. The lecture will follow the developments on the emerging field of x-ray quantum optics and focus on the mutual control of coherent x-ray radiation and nuclear transitions in this new regime of laser-matter interactions. [more]

MPSD Seminar

13671 1523535751

Short Course on: Ultrafast Spectroscopy of Phonons and Spin Excitations in Solids - Lecture VI

Lecture VI Abstract will follow. [more]

MPSD Seminar

14266 1528122902

Synchrotron Radiation from an Accelerating Light Pulse

Synchrotron radiation is regularly generated at large-scale facilities where GeV electrons move along kilometer-long circular paths. Here, we use a metasurface to bend light and demonstrate synchrotron radiation produced by a sub-picosecond pulse, which moves along a circular arc of radius 100 μm inside a nonlinear crystal. The emitted radiation, in the THz frequency range, results from the nonlinear polarization induced by the pulse. The generation of synchrotron radiation from a pulse revolving continuously about a circular trajectory has profound implications for on-chip THz sources. We present the first step towards this realization. [more]

MPSD Seminar

13670 1523535570

Short Course on: Ultrafast Spectroscopy of Phonons and Spin Excitations in Solids - Lecture V

Lecture V Abstract will follow. [more]

MPSD Seminar

13667 1523535473

Short Course on: Ultrafast Spectroscopy of Phonons and Spin Excitations in Solids - Lecture IV

Lecture IV Abstract will follow. [more]

MPSD Seminar

14175 1526650641

Ultrafast Electron Diffraction and Microscopy with High-Coherence Beams

Time-resolved electron imaging, diffraction and spectroscopy are exceptional laboratory-based tools to trace non-equilibrium dynamics in materials with a sensitivity to structural, electronic and electromagnetic degrees of freedom. The capabilities of these approaches are largely governed by the quality of the beam of electrons used.This talk will discuss recent advances made by employing high-coherence ultrashort electron pulses from nanoscale field emitters, which substantially enhance the achievable image resolution in both real and reciprocal space. Two complementary developments with ultimate surface sensitivity and spatial resolution, respectively, will be presented, namely Ultrafast Low-Energy Electron Diffraction (ULEED) and Ultrafast Transmission Electron Microscopy (UTEM). Several recent examples of applying these methods to the observation of phase-ordering kinetics, the excitation of strongly-coupled fluctuation modes and the control of metastable states will be given. [more]

Disputation

14161 1526643739

Atomically resolved dynamics of correlated quantum systems

[more]

MPSD Seminar

13669 1527676435

Short Course on: Ultrafast Spectroscopy of Phonons and Spin Excitations in Solids - Lecture III

Lecture notes see 'more' [more]

MPSD Seminar

14106 1526396916

High-harmonic spectroscopy using bi-elliptical fields

Over the recent years, high-harmonic generation has established itself as a promising spectroscopic technique. Notable examples include the tomographic imaging of molecular wave functions [1], the tracking of nuclear dynamics [2], and the reconstruction of the attosecond time-scale electron dynamics in molecules [3, 4].All these applications, however, have been limited to laser fields with linear polarization. High harmonic generation has only recently been extended to circularly-polarized drivers by utilizing a technique known as bi-circular high-harmonic generation (BHHG) [5,6,7]. In this talk, I will demonstrate the spectroscopic applications of this technique to the study of structure and dynamics of gas-phase atoms and molecules in a self-probing manner. I will start with an analysis of the helicity asymmetry of BHHG in noble-gas atoms and then proceed by illustrating how BHHG can be applied to study dynamical symmetry-breaking in a time-dependent manner in the context of rotational and vibrational molecular motion.Extension of high-harmonic generation to the regime of highly-elliptical fields opens up the way towards the study of chiral phenomena in high-harmonic generation. In this work, circular dichroism in the range of 3-8 % is observed on randomly oriented methyl oxirane (C3H6O) molecules in the gas phase. This chiral sensitivity is attributed to the sub-cycle chiral electron dynamics involving excited states of the cation that take place during the electron continuum propagation. Finally, I will present a study of time-dependent chirality based on following the temporal evolution of circular dichroism during the course of an ultrafast photodissociation reaction. [more]

IMPRS-UFAST core course

12947 1523274010

The theory of electronic structure and molecular dynamics

The course provides an overview of molecular electronic structure theory, covering the Hartree-Fock method, many-body perturbation theory, multiconfiguration self-consistent field, configuration interaction, coupled cluster, and density functional theory. Also it will discuss how to treat the interaction of molecules with electromagnetic fields. After this, it will cover the basics of molecular dynamics. [more]

MPSD Seminar

13666 1527676589

Short Course on: Ultrafast Spectroscopy of Phonons and Spin Excitations in Solids - Lecture II

Lecture notes see 'more'. [more]

MPSD Seminar

13665 1527676604

Short Course on: Ultrafast Spectroscopy of Phonons and Spin Excitations in Solids - Lecture I

Lecture notes see 'more'. [more]

IMPRS-UFAST core course

9959 1507719384

Non-linear optics - IMPRS-UFAST core course

The course provides an overview of the working principles of nonlinear optics with a focus on the basic physical concepts. [more]

MPSD Seminar

13735 1523627150

A New Room Temperature Multiferroic in the Bi-Fe-O System

Multiferroic materials, which exhibiting simultaneously two or more coupled ferroic orders, are attracting extensive research interest mainly due to their promising device applications in low power electronics and the exotic physics involved. Despite the fact that an increasing number of multiferroics have been identified through two decades of diligent and creative studies, their low transition temperature or small magnetoelectric coupling strength has hindered direct device applications. Searching for materials with room-temperature ferroelectricity, a large enough magnetization and coupling between these two is still the Holy Grail for fundamental condensed matter research. In this talk, I will report a novel room temperature multiferroic in the Bi-Fe-O system. The material is comprised of a hitherto-unexplored, hexagonal crystalline structure with Bi2O3 layers separated by γ-Fe2O3 blocks, which blends the excellent ferroelectric and ferrimagnetic performances of BiFeO3 and γ-Fe2O3 together to form an exotic multiferroic material with ferroelectric and ferrimagnetic transition temperature of above 760 K and 600 K, respectively. A combination of experimental and theoretical studies reveals that the polar state stems from the two dissimilar Bi sites and extends further into oxygen ions with the exquisitely modulated structure. This finding identifies a novel strategy for the realization of high-temperature multiferroicity and paves the pathway for the realization of practical room temperature magnetoelectric devices. [more]

MPSD Seminar

13799 1523963295

Resonant Thermalization of periodically driven strongly correlated electrons

[more]

MPSD Seminar

MPSD Seminar

13446 1522938563

Liquid-Phase Electron Microscopy of Cells and Nanomaterials in Liquid

Transmission electron microscopy (TEM) has traditionally been associated with the study of thin solid samples in vacuum. With the availability of reliable thin membranes of silicon nitride, TEM of liquid specimens has become accessible with nanoscale resolution in the past decade [1]. The usage of scanning transmission electron microscopy (STEM) presents a novel concept to study membrane proteins within whole mammalian cells in their native liquid environment [2]. The cells in liquid are placed in a microfluidic chamber enclosing the sample in the vacuum of the electron microscope, and are then imaged with STEM. It is not always necessary to enclose the cells in the microfluidic chamber. For many studies, it is sufficient to obtain information from the thin outer regions of the cells, and those can be imaged with high resolution using environmental scanning electron microscopy (ESEM) with STEM detector [3]. A third option is to cover a liquid specimen under a thin membrane of graphene providing the thinnest possible layer [4]. Liquid STEM was used to explore the formation of HER2 homodimers at the single-molecule level in intact SKBR3 breast cancer cells in liquid state [3]. HER2 is a membrane protein and plays an important role in breast cancer aggressiveness and progression. Data analysis based on calculating the pair correlation function from individual HER2 positions revealed remarkable differences its functional state between rare- and bulk cancer cells with relevance for studying the role of cancer cell heterogeneity in drug response. We discovered a small sub-populations of cancer cells with a different response to a prescription drug [5]. Liquid STEM was also used to explore the behavior of nanoparticles in liquid in time-lapse experiments. It was discovered that nanoparticle movement in close proximity of the supporting silicon nitride membrane was three orders of magnitude slower than what was expected on the basis of Brownian motion for a bulk liquid [6], pointing to the existence of a layer of highly ordered liquid at the membrane. References [1] de Jonge, N. and Ross, F.M. Nat. Nanotechnol., 6, 695-704 (2011) [2] de Jonge, N., et al. Proc. Natl. Acad. Sci., 106, 2159-2164 (2009) [3] Peckys, D.B., et al. Sci. Adv., 1, e1500165 (2015) [4] Dahmke, I.N., et al. ACS Nano, 11, 11108-11117 (2017) [5] Peckys, D.B., et al. Mol. Biol. Cell, 28, 3193-3202 (2017) [6] Verch, A., et al. Langmuir, 31, 6956–6964 (2015) [more]

MPSD Seminar

13505 1522938489

Sub-optical-cycle control of light and matter

[more]

MPSD Seminar

13503 1522937711

Slow-Electrons Interacting with Light and Matter

[more]

MPSD Seminar

13387 1522938521

Numerically exact full counting statistics of the Anderson impurity model

The full characterization of charge transfer processes in molecular junctions requires techniques for evaluating not only the first and second moments of charge currents, but also higher-order statistical cumulants of the charge transfer process. The complete set of cumulants gives access to the full counting statistics (FCS) through the so-called generating function [1]. [more]

IMPRS-UFAST core course

12603 1522925648

Ultrafast techniques

The course focuses on the use of modern light/ X-ray/ electron sources for investigating the physics/ chemistry/ biology phenomena. We will discuss scattering and image reconstruction techniques, spectroscopy and their use for time-resolved measurements . Key questions addressed are which techniques exist, how to use them, and which method is best used to reach a certain goal. [more]

CFEL Theory Seminar

13388 1522938591

Polariton photophysics and photochemistry: theoretical perspectives

Organic molecules interact strongly with confined electromagnetic fields in plasmonicarrays or optical microcavities owing to their bright transition dipole moments. Thisinteraction gives rise to molecular polaritons, hybrid light-matter quasiparticles.Molecular polaritonics opens new room-temperature opportunities for the nontrivialcontrol of energy transport in the nano and mesoscales and modification of physicochemicalproperties of molecular assemblies. In this talk, I’ll showcase some of theseopportunities that we have been theoretically exploring in the past few years within thecontext of physical chemistry. I’ll start by briefly mentioning our work on topologicallynontrivial phases in excitonic and polaritonic systems of organic dye molecules [1,2].Next, I will discuss recent work on how polaritons can enhance singlet-fissionprocesses [3] or how excitation energy can be transferred across mesoscopicdistances of hundreds of nanometers to micron lengthscales [4]. If time permits, I’llconclude by explaining what we can learn about molecular polaritons using twodimensionalspectroscopy [5,6].[1] J. Yuen-Zhou et al., Nature Mater. 13, 1026 (2014).[2] J. Yuen-Zhou et al., Plexcitons: Dirac points andtopological modes, Nat. Commun. 7, 11783 (2016).[3] L. A. Martínez-Martínez, et al., Polariton-assistedsinglet fission in acene aggregates, under review in J.Phys. Chem. Lett., arXiV:1711.11264.[4] M. Du et al., Polariton-assisted remote energy transfer(PARET), under review in Chem. Sci., arXiv:1711.11576.[5] B. Xiang et al., Revealing hidden vibration polaritoninteractions by 2D IR spectroscopy, under review in Proc.Nat. Acad. Sci., arXiv:1711.11222.[6] R. F. Ribeiro et al., Theory for nonlinear spectroscopyof vibrational polaritons, submitted to J. Phys. Chem.Lett., arXiv:1711.11576. [more]

IMPRS-UFAST Ph.D. Seminar

12949 1518598221

Good Scientific Practice for PhD students

In public, "good scientific practice" is often connected with cases of plagiarism when it comes to dissertations. However, the important topic covers a substatially wider spectrum of scientific conduct: Dealing with data (including checking, recording, ownership and storage), the publishing process and authorship, responsible supervision, academic cooperation, conflicts of interest and dealing with conflicts. Inappropriate academic behaviour includes inventing or faking data, violating intellectual property (theft of ideas or plagiarism) and sabotating the research of others. More subtle topics, such as skepticism, critical thinking, reproducibility, handling creativity, the danger of axiomatic assumptions and confirmation bias represent the "heart of good scientific practice". Every PhD student should have a professional understanding of all mentioned topics. [more]

MPSD Seminar

IMPRS-UFAST Ph.D. Seminar

12948 1518598322

Navigator workshop! Career orientation and job contacts: How to find your perfectjob outside academia

Thinking about your career after the PhD? Three half-days of explorations and personal encounters with visits to leaders from different sectors of work in Hamburg. This workshop will broaden your perspective - on what you have to offer and where you might go. [more]

IMPRS-UFAST focus course

10071 1503484768

Topological band theory - IMPRS-UFAST focus course

This course covers basic concepts in the topological classification of band structures of solids, the development of which led to the Physics Nobel Prize in 2016 for Thouless, Kosterlitz and Haldane. [more]

MPSD Seminar

12449 1515660508

Takashi Oka - Applied Floquet engineering

[more]

IMPRS-UFAST skills course

11523 1510140940

Presentation skills

“Poets are born – speakers are made.” Public speaking is a necessity in scientific life. Take part in this 2-day course, find out what your strengths are and develop your individual presentation profile. Take steps to learn how to lead the audience from your first appearance on stage until the last question in the discussion. Be authentic, enthusiastic and convincing! [more]

MPSD Seminar

12436 1515576330

Mitsuharo Uemoto - TDDFT+Maxwell multiscale method for lightpropagation calculation in semiconducting media

[more]

MPSD Seminar

11778 1512642696

Hélène Seiler - Development of an “optical NMR” spectrometer to investigate electronic couplings in molecules and nanostructures

Coherent Multi-Dimensional Spectroscopy (CMDS) is a powerful technique that is directly sensitive to couplings between quantum states. In the optical regime, the technique is well-suited to investigate interactions between the electronic degrees of freedom in systems such as biological light-harvesting complexes and nanostructures. Following a general introduction on Multi-Dimensional Spectroscopy, I will present an ultrafast optical two-dimensional spectrometer based on a hollow-core fiber for broadband visible continuum generation and two acousto-optic pulse shapers arranged in a Mach-Zehnder interferometer for the production of fully-coherent pulse trains. The setup can easily switch between a pump-probe geometry and a collinear geometry with polarization shaping capabilities. The methodological improvements presented here represent important enabling steps towards the longstanding goal of achieving an ”Optical NMR”, and extends the realm of all-optical Multi-Dimensional Spectroscopy to spatially heterogeneous samples. The methods developed are then applied on two classes of systems. The model system Nile Blue is used to validate the performance of the instrument. The spectrometer is also used to reveal new processes in colloidal semiconductor CdSe nanocrystals. One of the most fascinating aspects of semiconductor nanocrystals is their ability to host multiple excitations per particle. When multiple excitons are created in the same nanocrystal, bound quasi-particles called multiexcitons form. In contrast to the single exciton, the structural and dynamic properties of multiexcitons remains, to this day, relatively poorly understood due to their complexity. In the last part of the seminar, I will discuss new insights gained on the structure of the ground state biexciton thanks to the optical CMDS method. [more]

MPSD Seminar

11800 1512997248

Franco Bonafé - Time-dependent electron-nuclear dynamics in DFTB+: theory and applications

This seminar will be focused on an implementation of electron-nuclear real-time dynamics within the Density Functional Tight-Binding (DFTB) formalism in the DFTB+ package[1], as a result of a collaboration between the Quantum Dynamics Group (University of Córdoba) and the BCCMS (University of Bremen). Some theory details will be presented as well as its application to explain the launching of mechanical oscillations in metal nanoparticles under plasmon-resonant laser illumination[2]. [more]

MPSD Seminar

11637 1511190809

Michael Zürch - Photoexcitation dynamics in semiconductors and two-dimensional semiconductors observed by attosecond core-level spectroscopy

Investigation of the ultrafast photoexcited electronic response in semiconductors has provided invaluable insights into carrier dynamics. Germanium and its alloys with Si have promise for creating multi-junction solar cells with higher efficiency and mid-infrared optoelectronics. However, the dynamics are complicated by multiple energetically similar valleys, rendering an understanding of carrier thermalization and population inversion following photoexcitation difficult. Attosecond transient absorption spectroscopy (ATAS) has recently been employed to probe ultrafast electron and hole dynamics in germanium at the M4,5-edge (~30 eV). In the experiment, a 5 fs VIS-NIR pump pulse excites carriers across the direct band gap and the dynamics are probed with a time-delayed broadband extreme ultraviolet pulse generated by high harmonic generation in xenon spanning ~20-45 eV. The observed transient absorption signal contains the energetic distribution of both carriers, electrons and holes, due to state blocking as well as spectroscopic features induced by bandshifts (e.g. due to band gap renormalization) and broadening (e.g. due to many body effects). By iterative procedures the measured signal can be successfully decoupled into these contributions resolving the carrier and band dynamics with excellent time and energy resolution. Hot carrier relaxation on a 100-fs time scale and carrier recombination on a 1-ps time scale are observed in nanocrystalline Germanium. Going from bulk semiconductor to two-dimensional layers, long-lived core-exciton states are observed at the MoN2,3 edge between 32 and 35 eV in MoS2. Comparing the XUV absorption spectra of bulk and monolayer MoS2, a ~4 eV red-shift suggests a tightly bound core-exciton. The lifetime of the core-exciton states can be directly measured in the time domain. Furthermore, transient Stark shifts, coherences, and coherent population transfer between different core-exciton states are observed. [more]

MPSD ARD Seminar

11578 1510738568

Kay Gruenewald - Structural cell biology of virus-host interactions - an integrative approach

[more]

MPSD Seminar

11752 1512401673

Eric Heller - Graphene Spectroscopy and Ultrafast Pump-Probe Experiments and Theory

Graphene is a key reduced dimensionality solid with many promising applications. Its spectroscopy is vital to understanding the quantum physics of graphene and to evaluate some of the potential uses of graphene. We have found that new and very different interpretations of graphene spectroscopy and ultrafast pump-probe experiments are required. This will be explained. They are very informative about the role of phonon assisted processes in solids and the role of the electronic transition matrix elements. [more]

MPSD Seminar

11435 1512642302

Paolo G. Radaelli - Lecture 8: “Physical” tensors

[more]

MPSD Seminar

11434 1509550553

Paolo G. Radaelli - Lecture 7: Tensors and tensor products of representations

[more]

MPSD Seminar

11716 1511959262

Daniele Fausti - Optical control and quasiparticle witnessing in strongly correlated electron systems

The prospect of “forcing” the formation of quantum coherent states in matter, by means of pulsed electromagnetic fields, discloses a new regime of physics where thermodynamic limits can be bridged and quantum effects can, in principle, appear at ambient temperatures. In this presentation I will introduce the field of optical control of correlated electron systems. I will focus on the possibility of coherently driving low-lying excitations of quantum many body systems making light-based control of quantum phases in real materials feasible. I will review the recent results in archetypal strongly correlated cuprate superconductors and introduce our new approach to go beyond mean photon number observables. I will show that quantum features of light can provide a richer statistical information than standard linear and non-linear optical spectroscopies. This will potentially uncover with unprecedented detail the evolution and properties of light-induced transient states of matter.ReferencesScience 331 (6014), 189 (2011)Nature Comm. 6, 10249 (2015)Nature Comm. 5, 5112 (2014)New J. Phys. 16 043004 (2014)Nature materials 12 (10), 882-886(2013) [more]

MPSD ARD Seminar

11638 1511190893

Shaul Mukamel - Ultrafast Multidimensional Spectroscopy of Molecules with x-ray pulses and Quantum Light in Microcavities

Multidimensional spectroscopy uses sequences of optical pulses to study dynamical processes in complex molecules through correlation plots involving several time delay periods. Extensions of these techniques to the x-ray regime will be discussed. Ultrafast nonlinear x-ray spectroscopy is made possible by newly developed free electron laser and high harmonic generation sources. The attosecond duration of X-ray pulses and the atomic selectivity of core X-ray excitations offer a uniquely high spatial and temporal resolution. Stimulated Raman detection of an X-ray probe may be used to monitor the phase and dynamics of nonequilibrium valence electronic state wavepackets created by e.g. photoexcitation, photoionization and Auger processes. Novel ultrafast X ray probes for strongly coupled electron-nuclear dynamics , techniques based on a coherent stimulated Raman process that employs a composite femtosecond/attosecond X-ray pulse to directly detect the electronic coherences (rather than populations) , and new imaging techniques based on x-ray diffraction from electronic coherence will be presented. Nonlinear optical signals induced by quantized light fields and entangled photon pairs are presented. Conventional nonlinear spectroscopy uses classical light to detect matter properties through the variation of its response with frequencies or time delays. Quantum light opens up new avenues for spectroscopy by utilizing parameters of the quantum state of light as novel control knobs and through the variation of photon statistics by coupling to matter. Entangled-photon pairs are not subjected to the classical Fourier limitations on the joint temporal and spectral resolution. Strong coupling of molecules to the vacuum field of micro cavities can modify the potential energy surfaces thereby manipulating the photophysical and photochemical reaction pathways. Crossings of electronic potential surfaces in nuclear configuration space, known as conical intersections, determine the rates and outcomes of virtually all photochemical molecular processes. Strong coupling of molecules to the quantum vacuum field of micro cavities that can be used to manipulate their photophysical and photochemical reaction pathways and polariton relaxation in photosynthetic antennae are demonstrated. [more]

MPSD ARD Seminar

11596 1510835281

Thomas Renger - Structure-based theory of light-harvesting in photosynthesis

Two challenges in the simulation of excitation energy transfer and optical spectra of pigment-protein complexes are the equal magnitude of the excitonic and the exciton-vibrational coupling and the structure-based parametrization of the Hamiltonian (for review see ref. 1). We have developed quantum chemical/electrostatics/normal mode analysis (NMA) schemes to calculate optical transition energies of pigments in their binding site in the protein (site energies), interpigment excitonic couplings and the spectral density of the pigment-protein coupling. Our NMA of the spectral density shows that the modulation of site energies is an order of magnitude stronger than that of the excitonic couplings and that also in the basis of delocalized exciton states the diagonal exciton-vibrational coupling dominates [2]. This result explains the good performance of our earlier time-local lineshape theory [3], in which the diagonal elements are treated exactly and the off-diagonal elements in Markov and secular approximations, and triggered a new development that takes into account the finite relaxation time of nuclei during exciton relaxation [4]. I will give a summary of our theory development and present applications on a small model system (water soluble chlorophyll binding protein -WSCP) and large photosystem II core particles. In the case of WSCP we have developed and applied a theory of holeburning spectroscopy [5] that goes beyond the standard two-level system approach and allows for a quantitative description of experimental data, revealing the lifetime of the upper exciton state, in excellent agreement with results from 2D electronic spectroscopy and our earlier prediction [6]. In the case of photosystem II I will present results of the parametrization of the exciton Hamiltonian of its subunits [7-9]. These parameters were used to describe VIS/IR pump-probe data on single crystals of PSII core particles [10] that allowed for a verification of our earlier prediction [11] on the relative timescale of excitation energy and charge transfer in this system. The results are discussed in terms of photoprotection scenarios that allow photosystem II to switch between a light harvesting and an excitation energy quenching mode protecting the reaction center. [more]

MPSD Seminar

11671 1511527277

Binghai Yan - Nonlinear optical responses of Weyl semimetal materials

In the band structure of a Weyl semimetal (WSM), the conduction and valence bands cross each linearly through Weyl points that are usually treated as “monopoles” of the Berry curvature. As a second-order response, WSMs were very recently demonstrated to show strong nonlinear optical effects including an exotic nonlinear Hall effect. This is caused by the non-equilibrium distribution of the Berry curvature, described as the “dipole” of the Berry curvature. In this talk, I will talk about our recent computational results on nonlinear response for representative WSM materials TaAs and MoTe2. [more]

Joint Career Days: Career after your PhD

11326 1508755198

Career after your PhD - Academia, industry or science management?

On day one you will meet scientists as well as people from industry, NGOs and science management! Our speakers will share their experience regarding their doctoral studies and discuss career opportunities with you. On day two you may participate in workshops and coaching sessions on: Career coaching, career development, CV check, grant writing, funding consulting and science management. [more]

MPSD Seminar

11433 1509550577

Paolo G. Radaelli - Lecture 6: Projectors, subduction and group product

[more]

IMPRS-UFAST focus course

10070 1503484718

Superconductivity - IMPRS-UFAST focus course

This course covers the basic phenomenology and microscopic theory of superconductivity: - definition of superconductors and their thermodynamics - microscopic BCS theory: electron-phonon interaction, Fröhlich Hamiltonian, Cooper instability, mean-field theory, Bogoliubons [more]

MPSD Seminar

11432 1509363745

Paolo G. Radaelli - Lecture 5: Applications of representations to physics problems

See 'more' for link for lecture notes and supportin material. [more]

MPSD Seminar

11398 1510224834

Paolo G. Radaelli - Lecture 4: Key theorems about irreducible representations

[more]

MPSD Seminar

11397 1509550688

Paolo G. Radaelli - Lecture 3: Introduction to the theory of representations

[more]

Info meeting for PhD students on Bahrenfeld Campus

11327 1508762218

Last steps of your PhD - Info meeting

Are you about to finish your PhD? In this info meeting you will learn important facts for the last stage of your PhD, including all questions with respect to authorship, publishing, open access costs or printing your thesis at DESY. [more]

MPSD Seminar

11522 1510136653

Michael Schüler: Nonequilibrium topological states traced by transient spectroscopies

Chern insulators exhibit fascinating properties which originate from the topologically nontrivial state characterized by the Chern number. How these properties are affected and manifest in the presence time-dependent perturbations is still a sparsely explored field of research. This applies,in particular, to quantum quenches between topologically distinct phases. Identifying robust measures of topology which are applicable in nonequilibrium scenarios — ideally also for correlated materials or dissipative systems — is thus a nontrivial task. [more]

MPSD Seminar

11396 1509550707

Paolo G. Radaelli - Lecture 2: Crystallographic point groups and group theory

[more]

MPSD Seminar

11395 1509550508

Paolo G. Radaelli - Lecture 1: Introduction to symmetry in CMP

[more]

Disputation

11249 1507637464

Gengji Zhou - Power scaling of ultrafast mid-IR source enabled by high-power fiber laser technology

[more]

MPSD Seminar

11146 1506609308

Hideo Aoki - Quantum phases induced by polarised light --- Floquet-topological states and Higgs modes

Putting materials out of equilibrium can produce new quantum phenomena. When driven by a circularly-polarised laser, a massless Dirac system such as graphene can be converted into the Floquet topological insulator of photon-dressed electrons, which realises the quantum anomalous Hall effect. The phase diagram becomes increasingly intricate for lower laser frequencies where transitions between different Chern numbers take place. If we consider electron correlation, we can predict transitions between Floquet topological insulators and Mott insulator[1]. In another avenue a linearlypolarised light can induce the collective Higgs amplitude mode in superconductors, a condensed-matter analogue of the renowned particle. Then a resonantly strong third-harmonic generation arises, where the Higgs mode contribution is shown to dominate[2] unlike in the BCS approximation.[1] T. Mikami et al, Phys. Rev. B 93, 144307 (2016).[2] R. Matsunaga et al, Phys. Rev. B 96, 020505(R) (2017). [more]

IMPRS-UFAST Ph.D. Seminar

11077 1505816704

IMPRS-UFAST Ph.D. Seminar

[more]

IMPRS-UFAST skills course

11224 1516104770

IMPRS Job Seminar

You are not sure yet what to do after your PhD? You want to know what kind of jobs are out there in the real world? You wonder what makes you interesting for industry? Then this seminar is the right fit for you!In this seminar you have the chance to quiz interesting people from outside of academia. Find your dream job! Or at least know where to look for it. [more]

IMPRS-UFAST core course

9888 1503484514

Basics of chemistry and biochemistry - IMPRS-UFAST core course

In this course, chemistry will mainly be understood as reactions. The course gives an overview about the basics of reaction chemistry and discuss what is already known and what can be measured in the laboratory nowadays (i.e. describing the current frontiers and where the research performed at CFEL can make a difference). In the biochemistry part, the basic principles of nucleic acids (DNA, RNA, their replication etc.) and proteins, their structure and function etc. will be discussed. It will be interesting to work out where the new coherent sources can advance the field. [more]

MPSD ARD Seminar

11058 1505464396

Lipeng Chen - Theory meets spectroscopy: ensemble and single-molecule spectroscopic studies of ultrafast energy transfer processes in light harvesting systems

To a large extent, our knowledge of the photoinduced dynamics of molecular systems at the atomic level is shaped by nonlinear femtosecond spectroscopy. Traditionally, nonlinear femtosecond spectroscopy is an ensemble spectroscopy, performed on ensembles of identical chromophores in the gas phase or in the liquid phase. Modern femtosecond spectroscopy comprises a set of various third-order or higher-order technique including, for example, fluorescence up conversion, transient absorption, and photon echo spectroscopy. Very recently, the portfolio of femtosecond techniques has been extended towards singlemolecule detection by the development of fluorescence-detected double-pump singlemolecule spectroscopy. With this technique, a temporal resolution of about ten femtoseconds has been achieved. The technique permits the real-time monitoring of not only electronic populations, but also of electronic and vibrational coherence for individual molecules. [more]

IMPRS-UFAST skills course

10759 1503484206

Moderation training

Learn powerful and effective methods for conducting all types of meeting from an experienced expert. [more]

MPSD ARD Seminar

11078 1505730930

Shinji Saito - Supercooled water: Fluctuation, glass transition, and vibrational entropy

Water is the most common liquid. Its properties are not, however, common. Since the anomalies of water become pronounced at low temperatures, especially below its melting temperature, it has been proposed that the anomalous properties are attributed to the presence of two liquid states corresponding to the two amorphous ices. Experimental studies of supercooled water are however very difficult. This is due to the fact that bulk water is easily transferred to a crystalline phase in the “no man’s land”, which is a temperature range bounded by the crystallization of supercooled water at ~235K and by that of highly viscous liquid water at ~150K. Therefore, various theoretical and computational studies have been conducted for understanding the properties in the no man’s land. We have performed extensive molecular dynamics simulations from normal liquid to deeply supercooled states to reveal the structural and dynamical instabilities in the no man’s land. The spatiotemporal fluctuations, dynamic transition, glass transition, and vibrational contribution to Kauzmann temperature of supercooled water will be discussed. [more]

IMPRS-UFAST focus course

9887 1503484695

Intermolecular interactions - IMPRS-UFAST focus course

Within this focus course, we will study the basics of intermolecular interactions. These include molecular properties such as polarizabilities, to learn about the behavior of molecules in external fields, as well as the treatment of thermodynamic and statistical effects. [more]

MPSD Seminar

10945 1504190938

Sangwan Sim - Ultrafast optical spectroscopy of topological insulators and two-dimensional transition metal dichalcogenides

Ultrafast optical spectroscopy of quantum materials uncovers their intrinsic physical properties such as light-matter interactions and dynamics of particles and quasi-particles. In this presentation, I will present our ultrafast optical studies of two different electronic systems: topological insulators (TIs) and two-dimensional transition metal Dichalcogenides (2D TMDs). In TIs, where Dirac-like topological surface states (TSSs) coexist with an underlying bulk insulator, we have investigated ultrafast dynamics of TSS Dirac fermions and plasmons, and their interactions with phonon by using optical-pump terahertz-probe spectroscopy. We have found that, unlike Dirac electrons in graphene, TSS Dirac electrons exhibit unique dynamic features originating from interactions with coexisting bulk insulator. In the studies of 2D TMDs, we have performed ultrafast optical pump-probe spectroscopy of anisotropic excitons in group-VII TMDs. We discuss coherent light-matter interactions such as excitonic optical Stark effect and quantum beats, both of which exhibit significant laser-polarization dependence, resulting from anisotropic nature of the excitons. [more]

MPSD Seminar

10996 1504601420

Lukas Müchler - Exploring topological phenomena in Molecules

The use of topological methods has revolutionized the field of condensed matter physics both theoretically and experimentally. Many new exotic states of matter with unremovable surface states that can carry dissipationless currents have been predicted and quickly been verified experimentally. Moreover, topological techniques that characterize periodic Hamiltonians according to their spatial and non-spatial symmetries have lead to an almost complete classification of all possible non-magnetic states of matter that can be realized in crystals. [more]

MPSD Seminar

10930 1504601626

Ryan Requist - Reduced formula for the macroscopic polarization including quantum Fluctuations

The macroscopic polarization of a solid is an fundamental quantity from which permittivity and piezoelectric tensors can be derived. The Berry phase formula of King-Smith and Vanderbilt expresses the macroscopic polarization in terms of the Bloch states of a mean-field band structure, almost invariably taken from density functional theory. Although this procedure has been successful for many materials, quantum fluctuations cause it to break down in strongly correlated systems. [more]

Disputation

10437 1499254033

Frederike Ahr - High energy multi-cycle terahertz generation

[more]

IMPRS-UFAST skills course

10399 1503484078

Science Slam Workshop (IMPRS-UFAST skills)

You are proud of what you’re working on and want to know how to explain your research and promote yourself in an exciting way? Then this workshop is the right fit for you! In this Science Slam workshop you will learn to identify what makes you and your work fascinating. Find your personal style to blow your audience’s mind! [more]

MPSD Seminar

10479 1500033194

Lena F. Kourkoutis - New frontiers in cryo-electron microscopy: From Probing Low Temperature Electronic Phases to Processes at Liquid/Solid Interfaces

Spectroscopic mapping by STEM/EELS has proven to be a powerful technique for determining the structure, chemistry and bonding of interfaces, reconstructions, and defects. So far, most efforts in the physical sciences have focused on room temperature measurements where atomic resolution mapping of composition and bonding has been demonstrated [1-3]. For many materials, including those that exhibit electronic and structural phase transitions below room temperature and systems that involve liquid/solid interfaces, STEM/EELS measurements at low temperature are required. Operating close to liquid nitrogen temperature gives access to a range of emergent electronic states in solid materials and allows us to study processes at liquid/solid interfaces immobilized by rapid freezing [4,5]. [more]

CFEL Molecular Physics Seminar

10466 1500018011

Pedro de la Torre Luque - Study of cosmic neutrinos diffuse flux with Antares neutrino telescope: track channel

This project is based on the study of signals which ANTARES neutrino telescope have detected between 2007 and 2015. Firstly, an introduction about the sources of neutrinos and what we know about the origins of cosmic neutrinos is showed. Then, It will be explained the process of detection of neutrinos used by ANTARES neutrino telescope. Secondly, the analysis of the detected data in the 9 years mentioned before is carried out. The first part of the analysis consists in a comparison between detected data and simulated data will be shown for some variables, like neutrino direction or energy of them. The Monte Carlo simulated data is done in order to reproduce the observed Background and reduce it by applying cut-offs. Also the simulation of the expected signals from cosmic neutrinos is done to compare to the fitted background. The second part consists in the search of the cut-offs which will help to improve the signal/noise ratio. These cut-offs will be selected by mean of the analysis of some parameters or applying statistical methods, like Feldmann-Cousin method. Finally, the obtained signal is showed to extract conclusions. [more]

MPSD Seminar

10409 1498811861

Ming Lei - Capping the Ends: Structure and Function of Telomere Proteins

Telomeres, the natural ends of linear eukaryotic chromosomes, are specialized protein-DNA complexes that play essential roles in cell viability and genome integrity. The long-term goal of my research is to understand how telomeres protect chromosome ends and mediate their replication by telomerase. A six-protein complex, called shelterin, associates with telomeres and protects the ends of human chromosomes. A major gap in our knowledge of the shelterin complex is how its protein components organize at telomeres. I will present our recent studies that reveal the molecular architecture and functional significance of the shelterin complex. [more]

Disputation

10353 1498040291

Abid Hussain - Theory and computation of time-resolved spectroscopies for systems in complex environments

[more]

IMPRS-UFAST skills course

10069 1499768733

Intermediate C++ for PhD students - IMPRS-UFAST skills course

The ideal programming language for a physicist would allow him to write his code in terms of physical objects, like Hamiltonians and wave functions, with all the properties we expect of such objects, without sacrificing performance to highly optimised codes. [more]

10317 1497615596

Philipp Strasberg - Strong coupling thermodynamics and Markovian embedding strategies

Whenever a small-scale system is weakly coupled to macroscopic and Markovian reservoirs, it is possible to establish a consistent thermodynamic framework -- even for systems far away from equilibrium and even at the level of single, fluctuating trajectories. But outside the Markovian and weak coupling regime already the definition of basic quantities such as internal energy or heat becomes problematic. After reviewing the phenomenology of non-equilibrium thermodynamics, I will discuss a technique which allows to map a strongly coupled, non-Markovian system to a weakly coupled, Markovian one by appropriately including environmental degrees of freedom in the description of the system. Thus, by redefining the system-environment partition, it is possible to carry over a consistent thermodynamic framework to the strong coupling situation. [more]

Disputation

9882 1494248783

Alessandra Picchiotti - Coherent two-dimensional electronic broad-band UV-spectroscopy of DNA and its nucleobases

[more]

MPSD Seminar

10218 1496918622

Michael Lubasch - Density Functional and Tensor Network Theory

In my talk I will discuss this question: How can density functional and tensor network theory be combined in such a way that they benefit from each other. In particular I will present our publication [1] in which we developed a systematic procedure for the approximation of density functionals in density functional theory that consists of two parts. In the first part, for the efficient approximation of a general density functional, we introduced an efficient ansatz whose non-locality can be increased systematically. In the second part, we presented a fitting strategy that is based on systematically increasing a reasonably chosen set of training densities. I will present our results from reference [1] for strongly correlated fermions on a one-dimensional lattice. In this context we focused on the exchange-correlation energy and demonstrated how an efficient approximation can be found that includes and systematically improves beyond the local density approximation. Remarkably, we could show this systematic improvement for target densities that are quite different from the training densities. [1] M. Lubasch, J. I. Fuks, H. Appel, A. Rubio, J. I. Cirac, and M.-C. Banuls, New Journal of Physics 18, 083039 (2016)." [more]

MPSD Seminar

10121 1496325567

Yang Peng - Boundary Green functions of topological insulators and Superconductors

Topological insulators and superconductors are characterized by their gapless boundary modes. In this talk, we develop a recursive approach to the boundary Green function which encodes this nontrivial boundary physics. Our approach describes the various topologically trivial and nontrivial phases as fixed points of a recursion and provides direct access to the phase diagram, the localization properties of the edge modes, as well as topological indices. We illustrate our approach in the context of various familiar models such as the Su-Schrieffer-Heeger model, the Kitaev chain, and a model for a Chern insulator. We also show that the method provides an intuitive approach to understand recently introduced topological phases which exhibit gapless corner states. Ref: Yang Peng, Yimu Bao, Felix von Oppen, arXiv:1704.05862 (2017) [more]

10122 1496389364

Exhibition: Arts & Science in Hamburg’s City Hall

From 1 – 15 June 2017 the cluster of excellence CUI presents images from the micro world in Hamburg’s City Hall. The exhibition is centered around the beauty of visualizations of scientific phenomena and structures researched by the Hamburg Centre for Ultrafast Imaging, flanked by photographs of experiments and labs. [more]

Workshop

9042 1487063439

Non-equlibrium Quantum Matter - Workshop (Mainz)

This workshop will bring together leadings experts, both experimentalists and theorists, who are going to present some of the most exciting recent developments in non-equilibrium many-body physics.Topics will include light-induced superconductivity, topological Floquet states, solitons in superfluids, driven cold atom systems, and many more.If you would like to attend the workshop, please visit our webpage https://www.spice.uni-mainz.de/neqm-workshop-2017/ to find the preliminary program and the online application form, which has to be submitted before February 22nd. [more]

MPSD Seminar

9975 1494502987

Simon Wall - Spins, Phonons and Phase Separation in Correlated Materials

Electrons, phonons and spins are the key ingredients that make up correlated materials and understanding how these parameters interact is vital for determining their relative interactions. In this talk I will discuss our recent experiments on how to measure these interactions on a range of time and length-scales. I will discuss demagnetization of the antiferromagnetic Mott insulator Cr2O3 as measured through second harmonic generation, in which the demagnetization pathway is dictated by phonons. Then I will discuss the insulator to metal transition in VO2, both in terms of static nano-scale measurements of phase separation measured with resonant soft X-ray holography and dynamic measurements of how the phonon degree of freedom evolves away from the zone centre using time-resolved thermal diffuse scattering. [more]

Workshop

9422 1490089847

Workshops for PhD students on Bahrenfeld Campus - Conflict resolution skills

How to understand conflicts & solve them Conflicts appear in all areas of life and are sometimes inevitable. Since they are highly emotionally demanding, we often find it challenging to keep our mind clear and constructively think about a solution. [more]

Workshop

9421 1490089821

Workshops for PhD students on Bahrenfeld Campus - Strengths based leadership skills

The Workshop is about: Confident vulnerability. Helping individuals know what their strengths are and what they are not – and becoming comfortable with both. Confident vulnerability leaves individuals open, curious, willing to receive others’ perspectives and synergize through their differences. It is a necessary prerequisite to interdependence [more]

Workshop

9417 1494332458

Workshops for PhD students on Bahrenfeld Campus - The job interview - Business theatre with trained actors

A job interview is one of the most drawn-out and intimidating ways of making first impression. However, it’s also your opportunity to get on an employer’s good sight, which can give you a distinct edge over even those applicants whose credentials are better than yours. [more]

MPSD Seminar

9986 1494589193

Dante Kennes - Transient superconductivity from electronic squeezing of optically pumped phonons

Advances in light sources and time resolved spectroscopy have made it possible to excite specific atomic vibrations in solids and to observe the resulting changes in electronic properties but the mechanism by which phonon excitation causes qualitative changes in electronic properties, has remained unclear. Here we show that the dominant symmetry-allowed coupling between electron density and dipole active modes implies an electron density-dependent squeezing of the phonon state which provides an attractive contribution to the electron-electron interaction, independent of the sign of the bare electron-phonon coupling and with a magnitude proportional to the degree of laser-induced phonon excitation. Reasonable excitation amplitudes lead to non-negligible attractive interactions that may cause significant transient changes in electronic properties including superconductivity. The mechanism is generically applicable to a wide range of systems, offering a promising route to manipulating and controlling electronic phase behavior in novel materials. [more]

MPSD Seminar

9985 1494589059

Jorge Jover - Open quantum systems: a geometric description

In this talk, I will present some of the results in my PhD dissertation, whose main topic is the geometric description of open quantum systems. Differential geometry allows for an intrinsic formulation of mathematical models, thus achieving a better characterisation of their properties. I will analyse from a geometric perspective the manifold of pure and mixed states of quantum systems and its properties, such as its stratification in terms of the rank of states [1]. The algebraic properties of observables allow to define a Poisson and a symmetric tensor fields on the manifold, which are necessary in order to describe features such as dissipation and Markovian dynamics in an intrinsic way. Applications to Molecular Dynamics, in particular the Hamiltonian description of the Ehrenfest model, will also be discussed [2,3]. [1] Grabowski, Kus, Marmo. Symmetries, group actions and entanglement. Open Syst. Inf. Dyn. 13, 343–362 (2006) [2] Alonso et al. Statistics and Nosé formalism for Ehrenfest dynamics. J. Phys. A Math. Theor. 44 395004 (2011) [3] Alonso et al. Ehrenfest dynamics is purity non-preserving: a necessary ingredient for decoherence. J. Chem. Phys. 137 54106 (2012) [more]

Workshop

9419 1490089873

Workshops for PhD students on Bahrenfeld Campus - Competent at conferences

Conferences are a valuable opportunity to build your network of connections, but this doesn’t happen just by chance. Being able to initiate conversations and make a good impression quickly are key skills in making the most of your time at conferences. The Competent at Conferences workshop will teach you how to network effectively and productively at conferences, career fairs and other gatherings. [more]

Disputation

9881 1494229668

Irene Dornmair - Advanced Beam Dynamics and Diagnostics Concepts for Laser-Plasma Accelerators

[more]

MPSD Seminar

9822 1493737277

Eryin Wang - Novel and tailored electronic structures in 2D material heterostructures

The big family of 2D materials provides variable and interesting stacking blocksfor constructing 2D heterostructures to achieve novel electronic propertiesdistinct from its constitute materials. So far, the 2D material heterostructureshave been an emerging research area with increasing scientific interest. In thistalk, I will present the angle-resolved photoemission spectroscopy studies ontwo novel 2D heterostructures, Bi2Se3/BSCCO [1] and graphene/h-BN [2,3]. Iwill show how the proximity effect (in Bi2Se3/BSCCO) and moire superlatticepotential (in graphene/h-BN) tune the electronic properties and further lead tothe realization of many novel quantum phenomena. The variety of 2D materialsgenerates great possibilities in 2D heterostructures which are waiting for moreresearch investigations. [more]

Workshop

9105 1493737494

MPSD Workshop on Non-equilibrium phenomena at short length scales and in low dimensions

Invited Speakers: Jessica M. Anna, Dimitri N. Basov, Jacqueline Bloch, Andreas Heinrich, Shahal Ilani, Sebastian Loth (MPSD), Frank Koppens, Kurt Kremer, Abhay Pasupathy, Sebastian Schmidt, Tal Schwartz, Feng Wang. [more]

IMPRS-UFAST core course

7686 1518537449

Solid State Physics

From a microscopic point of view, a solid is just a regular arrangement of atoms, embedded in a soup of electrons. Yet, a remarkably rich manifold of phenomena emerges from this simple starting point, ranging from simple metals and semiconductors to multiple kinds of magnetic order or superconductivity. In this course we will discuss basic properties of solids and their microscopic understanding. [more]

MPSD Seminar

9683 1492611281

Sven Ahrens - Relativistic quantum dynamics and the electron spin in standing light waves

Strong laser beams allow for the coherent control of electrons, as for example electron diffraction in standing light waves [1]. In my talk I will discuss the possible manipulation of the electron spin in X-ray diffraction, in which the interacting standing wave of light can be formed from intensive and coherent X-ray beams from free-electron lasers [2]. The quantum dynamics of this process is theoretically modeled by inserting a plane wave ansatz for the electro-magnetic field and the electron wave function into the Dirac equation [3]. Based on this relativistic quantum description and substantiated by numeric and analytic solutions I will talk about the necessary kinematic conditions for generating spin effects in light-matter interaction. To the end I will present spin dynamics in circularly polarized laser fields [4,5] and discuss how circular polarization can be used for generating spin-dependent diffraction and spin polarization [6]. [1] D. L. Freimund, K. Aflatooni, H. Batelaan, Nature 413, 142 (2001). [2] S. Ahrens, H. Bauke, C. H. Keitel, and C. Müller, Phys. Rev. Lett. 109, 043601 (2012). [3] S. Ahrens, H. Bauke, C. H. Keitel, and C. Müller, Phys. Rev. A 88, 012115 (2013). [4] H. Bauke, S. Ahrens, C. H Keitel, R. Grobe, New J. Phys. 16, 103028 (2014). [5] H. Bauke, S. Ahrens, R. Grobe Phys. Rev. A 90, 052101 (2014). [6] S. Ahrens, arXiv:1604.06201 [quant-ph] (2016). [more]

MPSD Seminar

9631 1492007837

Peter Deák - How to choose the correct hybrid functional for defect calculations

The electronic and optical properties of a material critically depend on its defects, and understanding that requires substantial and accurate input from theory. Defect calculations in traditional semiconductors have relied on the local and semi/local approximations of density functional theory, which in wide band gap materials may lead to fatal errors. Since first-principle total energy methods beyond these approximations cannot yet be carried out with sufficient accuracy for the supercells needed in defect calculations, nowadays semi-empirical hybrid functionals are often applied instead. In my talk I will analyze the performance of the HSE06 screened hybrid functional on defects in Group-IV semiconductors and in TiO2, and show that its success is the result of error compensation between semi-local and non-local exchange, resulting in a proper derivative discontinuity (reproduction of the band gap) and a total energy which is a linear function of the fractional occupation numbers (removing most of the electron self-interaction). As it is well known, however, HSE06 does not work equally well for all materials. On the example of Ga2O3, I will show that tuning both the mixing and the screening parameter of HSE for the given material allows to ensure the same error compensation. Unless the electronic screening is strongly direction- or orbital-dependent (as in ZnO), the optimized HSE hybrid is nearly self-interaction free and provides a band structure on par with GW. Since the total energy can also be calculated, the real equilibrium structure of a defect can be found and the levels are in good agreement with experimental observations. [more]

March for Science

9579 1492779235

March for Science (non MPSD)

Just a little information about the March for Science which will also have a satellite march in the city of Hamburg (there will be no official MPSD participation). Further informations on the websites: https://www.marchforscience.com/ and http://marchforsciencehamburg.de [more]

IMPRS-UFAST skills course

8377 1484562419

Good scientific practice

Want to learn more about good scientific practice? This course wants to support doctoral students to develop a responsible professional conduct as researchers. You will gain a general understanding of good scientific practice and scientific misconduct. [more]

Nonlinear harmonic generation and ultrafast studies of perovskite iridates

9492 1490711760

Hao Chu - Nonlinear harmonic generation and ultrafast studies of perovskite iridates

The perovskite iridate Srn+1IrnO3n+1 realizes an interesting analogue to the cuprate high Tc superconductor. When electron-doped, the single-layer Sr2IrO4 is shown to manifest a pseudogap phase and possibly d-wave superconductivity. Using second harmonic generation rotational anisotropy, we show that near the antiferromagnetic transition there exists a magnetic multipolar order that breaks inversion symmetry in hole-doped Sr2IrO4. One candidate for this order is the loop current order that is predicted to exist in the pseudogap region of cuprate. In bilayer Sr3Ir2O7, electron-doping has been found to induce an insulator-to-metal transition in addition to a structural phase transition at low temperature. There has been no prior experimental evidence of electronic instabilities in the bilayer system. Using time-resolved optical reflectivity, we detect a charge-density-wave-like instability in metallic samples of electron-doped Sr3Ir2O7. The absence of signatures of a new spatial periodicity from diffraction, scanning tunnelling and photoemission based probes suggests an unconventional and possibly short-ranged nature of this density wave order. [more]

Disputation

9450 1490772321

Julia Hengster - Towards ultrafast time-resolved experiments with nanoscale objects and surfaces

[more]

MPSD Seminar

9630 1492007594

Noejung Park - Ab initio study of ultrafast dynamics of spin-valley polarized states in TMDC with a particular focus on the role of phonon

The valley degree of freedom and the possibility of spin-valley coupling of solid materials have attracted growing interest, and the relaxation dynamics of spin- and valley-polarized states has become an important focus of recent studies. In spin-orbit-coupled inversion-asymmetric two-dimensional materials, such as MoS2, it has been found that the spin randomization is characteristically faster than the time scales for inter- and intra-valley scatterings. In this talk, I present our recent study of the ultrafast non-collinear spin dynamics of the electron in a valley of monolayer MoS2 by using real-time propagation time-dependent density functional theory. We found that the spin precession is sharply selectively coupled only with the particular optical phonon that lifts the in-plane mirror symmetry. We suggest that the observed spin randomization can be attributed to this spin-phonon interaction. Further, our results imply that flipping of spins in a spin-orbit-coupled system can be achieved by the control over phonons. In a later part of the talk, I would also describe the feature of the computational package we have developed and have used for the spin-phonon dynamics, which is based on the plane-wave basis set and various types of pseudopotentials. [more]

MPSD Seminar

9551 1491314406

Vahid Sandoghdar - Nano-Quantum-Optics: from single photons and emitters to cooperative effects

I plan to start this presentation with an overview of our work over the past decade on the efficient coupling of light and single quantum emitters, leading to the single-photon communication of two individual molecules at long distances [1]. In this context, we will also discuss new results on a high-efficiency triggered source of single photons [2] and coherent nonlinear optical phenomena, which let a single organic molecule act as an efficient switch for weak beams of light [3]. The long-term goal of these projects is to establish a platform for nano-quantum-optical operations and cooperative interactions in a mesoscopic system of photons and quantum emitters [4, 5]. In order to achieve this, we have developed novel microcavity [6] and chip-based nanoguide circuitry [7] for use at cryogenic conditions.References:[1] Y. Rezus, et al., Phys. Rev. Lett. 108, 093601 (2012). [2] X-L. Chu, et al., Nature Photonics, 11, 58 (2017).[3] A. Maser, et al., Nature Photonics 10, 450 (2016).[4] S. Faez, et al., Phys. Rev. Lett. 113, 213601 (2014). [5] H. Haakh, et al., Phys. Rev. A, 94, 053840 (2016).[6] D. Wang, et al., Phys. Rev. X, under review.[7] P. Türschmann, et al., submitted. [more]

MPSD Seminar

9555 1491393638

Dr. Heloise Therien-Aubin - Engineering the interface of nanocolloids with polymers

In the design of nanocolloids for targeted applications, whether the nanoparticles are used as drug delivery vehicles or as filler in nanocomposites, it is crucial to control the stability, the miscibility and/or the self-assembly of the nanocolloids. In order to gain such control, the surface of the nanocolloid is frequently functionalized by tethering a corona of either small molecules or polymer chains. The nature and the composition of the corona formed by the tethered molecules dictate the interactions between the nanocolloids and their environment and thus the final behavior of the material. Nanoparticles functionalized with a corona of polymer brush were used in the design of hierarchically structured materials and displayed new collective properties. By varying the degree of polymerization, the grafting density and the chemical composition of the polymer chains, a variety of structures were obtained. We now want to establish a correlation between the mesoscopic properties observed in these nanoparticle-based systems with the properties, structure and dynamic of the polymer brush layer. [more]

MPSD Seminar

9535 1490969094

Michael Lorke - Carrier dynamics in MoS2

In the context of the current interest in transition-metal dichalcogenides, we study the optical generation and relaxation of excited carriers and their influence on optical properties. [more]

MPSD Seminar

9499 1490797894

Claudius Hubig - Time Evolution with a Krylov Variant for MPS Time Evolution with a Krylov Variant for MPS

I will briefly motivate the need for time-evolution methods on matrix-product states and provide an overview over the available methods. Focus will then be placed on the Krylov subspace method to evaluate exp(-tH)|ψ❭, starting from a naive translation of the standard method suitable for dense matrix-vector arithmetic to matrix-product arithmetic. Key improvements that can be made to the algorithm when applied to matrix-product arithmetics will then be illustrated, resulting in increased precision and reduced computational effort. [more]

IMPRS-UFAST Ph.D. Seminar

7740 1503491563

IMPRS-UFAST Ph.D. Seminar

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MPSD Seminar

9497 1490782354

Tong Zhou - Quantum Spin-quantum Anomalous Hall Effect with Tunable Edge States in Sb Monolayer-based Materials

The quantum anomalous Hall (QAH) effect, quantum spin Hall (QSH) effect and (quantum) valley Hall ((Q)VH) effect have attracted considerable attention in condensed matter physics and material science. Generally, only one of the QAH, QSH, and QVH effects can be realized in a specific system. It would be very interesting if these three effects can be achieved in one single system. In this talk, I shall represent this interesting imagination may be realized in Sb monolayer-based materials, where the QAH state occurs at one valley and the QSH state occurs at the other valley, called quantum spin-quantum anomalous Hall (QSQAH) effect. [more]

Disputation

9191 1488379539

Kemal Shafak - Large-scale laser-microwave synchronization for attosecond photon science facilities

[more]

IMPRS-UFAST core course

7687 1485872543

Ultrafast techniques

The course focuses on the use of modern light/ X-ray/ electron sources for investigating the physics/ chemistry/ biology phenomena. We will discuss scattering and image reconstruction techniques, spectroscopy and their use for time-resolved measurements . Key questions addressed are which techniques exist, how to use them, and which method is best used to reach a certain goal. [more]

IMPRS-UFAST skills course

9275 1488977950

Introduction to C++ for PhD students

In this C++ introductory course, you will completely learn the basic C++ syntaxes and will become familiar with object-oriented programming.As the course is going to be project-oriented, we will start by a physical problem from the beginning of the class and you will be instructed to implement a code to solve the problem during the course. [more]

MPSD Seminar

9128 1487771964

Ra’anan I. Tobey - Transient Grating Spectroscopy in Magnetic Thin Films: Elastic Excitation of a Transient Magnonic Crystal

Control of material properties is one of the driving forces in ultrafast optical sciences. The notion that light can influence material parameters is founded on a wide range of experiments demonstrating optomagnetic control, light induced superconductivity, and the photo induced insulator to metal transition in a wide range of materials. A recent addition to the tool chest of control methodologies is the excitation of acoustic waves, and their effect on intrinsic materials properties; particularly the material magnetization via magnetostrictive effects. [more]

Disputation

9034 1487062128

Eliza Casandruc - Nonlinear Optical Control of Josephson Coupling in Cuprates

[more]

MPSD Seminar

9220 1488812739

Michael Sentef - Light-enhanced electron-phonon coupling from nonlinear electron-phonon coupling

In light of recent experiments suggesting light-induced superconductivity [1] as well as light-enhanced electron-lattice coupling [2] for strongly driven IR phonons, it is natural to ask for a minimal and generic theoretical model that predicts such enhancement effects of important couplings in different material classes. One idea that comes to mind is nonlinear electron-phonon coupling [3,4]. A quadratic coupling term of the form " g2 nel x2IR " is generically the lowest order symmetry-allowed direct coupling of an IR-active phonon coordinate xIR to the electronic density nel in systems with inversion symmetry. In this talk I will present model evidence for light-enhanced electron-phonon coupling and light-induced effective attraction between electrons based on nonlinear electron-phonon coupling [3], the latter of which was already discussed in a similar context in [4]. [1] M. Mitrano et al., Nature 530, 461 (2016) [2] E. Pomarico et al., Phys. Rev. B 95, 024304 (2017) [3] M. A. Sentef, arXiv: 1702.00952 [4] D. M. Kennes et al., Nature Physics (2017) , doi:10.1038/nphys4024, arXiv:1609.03802 [more]

MPSD Seminar

9133 1487855304

Markus Kowalewski - Coherent Signatures of Conical Intersections in Ultrafast X-Ray Spectroscopy

The rates and outcomes of virtually all photochemical and photobiological processes are dominated by conical intersections (CIs), which provide a fast sub-100-femtosecond nonradiative pathway back to the ground state. At a CI, the electronic and nuclear degrees of freedom frequencies are comparable and strongly mix due to the breakdown of the Born-Oppenheimer approximation. [more]

MPSD Seminar

9129 1487774342

Kota Ido: " Time-dependent variational Monte Carlo method for nonequilibrium strongly correlated electron systems and its application "

Strongly correlated electron systems driven out of equilibrium have attracted much attention because of potential routes to realizing intriguing phenomena that are not attainable in the equilibrium. To treat such systems, we proposed a time-dependent trial wave function with many variational parameters for the time-dependent variational Monte Carlo method. To show the accuracy of our trial wave function in nonequilibrium states, we present our benchmark results for relaxation dynamics during and after interaction quench protocols of fermionic Hubbard models. We find that our trial wave function well reproduces the exact results for the time evolution of physical quantities such as momentum distribution and superconducting correlations. As its application, I will show the dynamics of d-wave superconductivity in two-dimensional correlated electron system under a laser irradiation. Our results show that the superconductivity can be enhanced by irradiating strong laser. I will discuss the origins of this enhancement associated with the laser effect and the relation between superconductivity and charge inhomogeneous phases. [more]

CFEL Molecular Physics Seminar

9037 1487064316

Yoni Toker: Watching Isolated Molecules Change Their Shape

Recently it has been shown that using two stages of ion mobility it is possible to measure isomerizations - structural changes in isolated molecules. Moreover, it is possible to measure the relative energies of different isomers and to deduce the barrier energy for each isomerization pathway. We have applied the technique to one of the most biologically important cases; that of the retinal protonated Schiff base (RPSB). RPSB is the chromophore which acts as a photon detector in every known form of animal vision. The primary step in vision is photoisomerization of the RPSB, which then activates the surrounding protein. We have studied the barrier energies for isomerizations of the RPSB and have shown them to be significantly lower than within the protein. We have also compared different derivatives of the chromophore and shown that slight changes to the structure of the chromophore, can dramatically effects its energy landscape. [more]

MPSD Seminar

9067 1487173496

Klaas Giesbertz - One-body reduced density matrix to potential mapping in finite basis sets at elevated temperatures One-body reduced density matrix to potential mapping in finite basis sets at elevated temperatures

Density functional theory in finite basis sets tends to degenerate to one-body reduced (1RDM) functional theory. As all calculations are done in finite basis sets, a rigorous foundation of 1RDM functional theory is desirable. To avoid uniqueness problems in the potential to 1RDM mapping, I will discuss the foundations of 1RDM functional theory in finite basis sets at finite temperatures, both for fermions and bosons. The fermionic case turns out to be relatively straightforward, but the bosonic case requires more care. The main result is that we can rigorously proof v-representability and functional differentiability in this setting. [more]

MPSD Seminar

9039 1487062924

Alexander Weismann: "Ballistic transport through magnetic atoms and molecules studied with conductance and shot noise spectroscopy"

The scanning tunneling microscope allows to build and study nanostructures at a single atom level. It can be further used to explore the ballistic electron transport regime by bringing the tip into contact with single atoms and molecules in a well-defined way. The measurement of quantum shot noise in nanoscopic contacts provides additional information on the underlying conduction processes and reveals a spin polarization of the current by single Fe and Co atoms between two gold electrodes. The impact of spin-orbit coupling on electron transport is demonstrated using single Ir atoms on a ferromagnetic substrate, where large changes of the anisotropic magnetoresistance are observed between the tunneling and the contact regime. In ballistic transport through a Mn-porphyrin molecule we demonstrate, that the voltage drop over the molecular junction moves from the tip-molecule gap to the molecule-substrate bond for higher conductances. This strongly modifies the shape of the measured Kondo resonance. [more]

MPSD Seminar

9024 1487072064

Niko Säkkinen - Application of Time-Dependent Many-Body Perturbation Theory to Excitation Spectra of Selected Finite Model Systems

Many-Body Perturbation Theory (MBPT) is a methodology routinely employed in computational spectroscopy to calculate photoemission and absorption spectra. However, usually these computational experiments are only possible for real nanostructures, solids, etc. by resorting to simple approximations in which, e.g., self-consistency is neglected. [more]

IMPRS-UFAST core course

7685 1480331440

Source technology

The course provides an overview of the working principles of modern light/ X-ray/electron sources, including the respective physics background and their currentstrengths and limitations. The focus will be on techniques and technical basics. [more]

IMPRS-UFAST skills course

7739 1484145442

Preparing for your PhD defence

In this workshop participants have the opportunity to strategically engage with the upcoming oral examination. They develop individual strategies for preparing themselves and learn techniques so they can direct the discussion even at critical points. [more]

CFEL Theory Seminar

8895 1486037106

Matteo Puviani - Strongly correlated Floquet systems: Cluster Perturbation Theory approach

Under the influence of periodic fields quantum systems may reach regimes inaccessible under equilibrium conditions and new phases may be engineered by a tunable control [1]. The coexistence of periodic driving forces and electron-electron correlation is particularly interesting for two main reasons: on one side the external driving effectively modulates the inter-site hopping enhancing the effects of the e-e repulsion and the tendency to an insulating behaviour. On the other hand, irradiation itself is responsible for a photo-doping consisting in an electronic energy dressing that may turn a Mott insulator into a metal. Due to these competing effects, novel phenomena are expected when strongly correlated quantum systems are exposed to time-dependent fields. [more]

MPSD Seminar

8389 1484647341

Tetiana Rokhmanova - Reflection, Transmission, and Transformation of Electromagnetic Waves in Layered Superconductors

The presentation aims to give a brief review of several theoretical works carried out for layered superconductors [1-4]. It will be shown that the dependence of the transmission coefficient of nonlinear THz waves on the incident wave amplitude shows hysteretic behavior both when the waves are propagating along and across superconducting layers. The polarization transformation of incident waves after their reflection and transmission through a layered superconductor can occur. However, there exist two waves with mutually orthogonal polarizations, which practically do not interact with each other even in the nonlinear case. Using these two mutually orthogonal polarizations, we study polarization transformation of nonlinear transverse electric and transverse magnetic waves. In addition, we show that external magnetic field can be effectively used to control transparency and polarization transformation in layered superconductors. [more]

IMPRS-UFAST core course

7688 1480331483

The theory of electronic structure and molecular dynamics

The course provides an overview of molecular electronic structure theory, covering the Hartree-Fock method, many-body perturbation theory, multiconfiguration self-consistent field, configuration interaction, coupled cluster, and density functional theory. Also it will discuss how to treat the interaction of molecules with electromagnetic fields. After this, it will cover the basics of molecular dynamics. [more]

Hamburg Photon Science Colloquium

6709 1479908856

Matthias Bartelmann - A microscopic theory for cosmic structures

Our Universe is permeated by a network of filamentary structures showing a remarkable degree of universality. When treated as a huge ensemble of correlated classical particles out of equilibrium, the properties and the evolution of these structures can be modelled and understood in a straightforward way. I shall describe a new theory for cosmic structures and first results obtained from it. [more]

ZOQ-Colloquium

8220 1484571656

Antoine Georges - Quantum Matter - from hot superconductors to cold atoms

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MPSD Seminar

8395 1484667961

Enrico Ronca - Theoretical Methods for Excited State Properties in Extended Systems

Light matter interaction is involved in several fundamental processes in Chemistry, Physics and Biology and is at the basis of Spectroscopy, experimental technique representing probably the most important source of information about properties of matter. Due to the significant improvements introduced in the last decades, spectroscopic techniques became very accurate and the interpretation of spectra, just by observation of the experimental results, became sometimes extremely complicated. For this reason the need of accurate theoretical methods able to reproduce and interpret the experimental results is becoming more and more pressing. The accurate theoretical simulation of spectra is therefore a very a challenging task, in particular for extended systems for which only approximated methods can be used. [more]

IMPRS-UFAST skills course

7738 1480512192

Getting tasks done

A PhD is a marathon not a sprint. The sheer number of different tasks that need to be done can sometimes be overwhelming. Being able to set goals, prioritise tasks and remain motivated are skills essential for the progression and achievement of your PhD. [more]

Hamburg Photon Science Colloquium

6708 1479908841

Justin Wark - Creating & Diagnosing Solid Density Plasmas with an X-ray FEL

4th generation light sources provide the capability to irradiate solids with X-rays at intensities in the range of optical lasers. At high focused intensities and sub-100 fs pulse lengths, solid targets transform to plasmas at several millions of degrees Kelvin. Detailed X-Ray spectroscopy allows us to probe the physics of these dense plasmas, and initial results have challenged our understanding of such basic details as how many bound states exist, and the rate at which collisions occur. It appears that current understanding of dense plasmas is woefully inadequate. [more]

MPSD Seminar

8291 1483606225

Ultrafast spintronics with terahertz radiation

Terahertz (THz) electromagnetic radiation is located in the gap that separates the realms of electronics (<1 THz) and optics (>30 THz). Sub-picosecond THz pulses are capable of probing and even controlling numerous low-energy excitations such as phonons, excitons and Cooper pairs. Here, we consider experiments showing that THz radiation is also a very useful and versatile tool in the fields of spintronics and ultrafast magnetism. First, we optically launch ultrafast spin transport and study its conversion into charge currents by means of the inverse spin Hall effect [Nature Nanotech. 8, 256 (2013)]. The charge current can be detected by sampling the concomitantly emitted THz radiation. This approach allows us to monitor ultrafast spin currents and provides a quick and easy estimate of the strength of the spin Hall effect in a contact-free manner. In addition, optimization of the spintronic structure has led to new, efficient and scalable emitters of THz pulses that fully cover the range from 1 to 30 THz without gap [Nature Photon. 10, 483 (2016)]. Second, we address spin-lattice coupling by selective excitation of optical phonons in the model ferrimagnetic insulator Y3Fe5O12 (YIG) and find a quenching of magnetic order on a time scale as short as 1 ps. This observation attests to a highly efficient coupling of crystal lattice and electron spins in this material. [more]

MPSD Seminar

7934 1481803065

Julian Gebhardt: Ab initio modeling of perovskite materials and two-dimensional organic networks

Perovskite materials with stoichiometry ABX3 are a rich family of ionic compounds with many technological interesting properties. They can be traditional inorganic, metal per- ovskites or hybrid perovskites with one organic cation. In this talk I want to discuss some results of a special modification of the latter kind, the so-called layered perovskites. This family of structures is currently rediscovered, and we report on the geometrical and electronic structure of one promising candidate ((C6H5C2H4NH3)2PbI4) with phenethylammonium cations on the A-site and compare the differences towards the benchmark case of three-dimensional (3D) hybrid perovskites, CH3PbI3. The influence of varying the cation as well as changing the dimensionality from 3D to 2D systems is discussed by comparing bulk and monolayer structures of both systems. In addition, insight into the optical behavior and the observed electron-phonon coupling will be given. [more]

Disputation

7862 1480927714

Wei Liu - Advanced ultrafast fiber laser sources enabled by fiber nonlinearities

[more]

Hamburg Photon Science Colloquium

6707 1479908826

Kwang S. Kim - Carbon based nano-optics, -electronics and -spintronics

I discuss the interplay between theory and experiment to design super functional carbon-based nanomaterials/nanodevices. These include intriguing organic nanostructures, graphene and functionalized carbon hybrid materials for energy harvesting, solar cells, fuel cells, gas storage, water remediation and medical treatment. Hyperresolution phenomena by nano-lensing, super-paramagnetism driven water remediation, and super-magnetoresitance & ultrafast DNA sequencing of graphene nanoribbon are addressed. [more]

MPSD Seminar

7874 1481126186

Michael Ridley - Partition-free theory of time-dependent current correlations in nanojunctions in response to an arbitrary time-dependent bias

Working within the Nonequilibrium Green's Function formalism, a formula for the two-time current correlation function is derived for the case of transport through a nanojunction in response to an arbitrary time-dependent bias. The one-particle Hamiltonian and the wide band limit approximation are assumed, enabling us to extract all necessary Green's functions and self-energies for the system, extending the analytic work presented previously [Ridley et al. Phys. Rev. B (2015)]. [more]

Informationsveranstaltung

7764 1479993831

Annual General Meeting at MPSD

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MPSD Seminar

7894 1481208735

Superconductivity in alkali doped fullerenes

In this very informal talk I will first briefly present our view on superconductivity in alkali doped fullerenes. In particular, I will discuss how it is at all possible that M3C60 has an s-wave condensate despite the sizeable intra-molecular Coulomb repulsion relatively to the narrow molecular bandwidth. In the second part of the talk I will review what it is known about the MIR optical properties of doped fullerenes and try to build a link with the remarkable Hamburg observation of a large enhancement of Tc under intense THz pumping. [more]

Hamburg Photon Science Colloquium

6706 1479908811

Hermann Dürr - Controlling spins in space and time

Magnetism is a quantum effect that has fascinated mankind for millennia and also led to many modern-day applications, very prominently in information processing and storage. Now available polarized soft X-ray pulses from X-FELs with sub-100 fs duration allow observing magnetic interactions at work in their natural length and timescales. I will show how the challenges for performing time-resolved XMCD at the Linac Coherent Light Source have recently been overcome and give an overview how such studies help to understand the fundamental speed limits for nanoscale spin motion. [more]

Disputation

7759 1480510083

Sharareh Sayyad - Nonequilibrium electron-lattice dynamics

[more]

Disputation

7815 1480510057

Khalid Siddiqui - Investigating photoinduced phenomena in molecular crystals with prospects for atomically-resolved dynamics

[more]

IMPRS-UFAST skills course

7691 1480511990

Presentation skills

“Poets are born – speakers are made.” Public speaking is a necessity in scientific life. Take part in this two-days course, find out what your strengths are and develop your individual presentation profile. Take steps to learn how to lead the audience from your first appearance on stage until the last question in the discussion. Be authentic, enthusiastic and convincing! [more]

Hamburg Photon Science Colloquium

6705 1479908795

Thomas Ebbesen - The Alchemy of Vacuum – Hybridizing Light and Matter

Strong coupling of light and matter can give rise to a multitude of exciting physical effects through the formation of delocalized hybrid light-matter states. After introducing the fundamental concepts, examples of modified properties under strong coupling, such as enhanced charge transport in organic semiconductors and non-radiative energy transfer, will be given to illustrate the broad potential of light-matter states. [more]

 
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