Event archive 2016

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

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 1526565562

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

Lecture II Abstract will follow. [more]

MPSD Seminar

13665 1526310568

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

Lecture I Abstract will follow. [more]

IMPRS-UFAST core course

12946 1523273664

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]

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

[more]

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

[more]

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

[more]

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]

MPSD Seminar

7763 1479993074

Cedric Weber - Many body effects in transition metal molecular systems

Phenomena that are connected to quantum mechanics, such as magnetism, transport, and the effect of impurity atoms and disorder, and their relation to material design and energy needs are important for almost every branch of the industry. Density functional theory (DFT) was successful at making accurate Predictions for many materials, in particular compounds which have a metallic behaviour. DFT combines high accuracy and moderate computational cost, but the computational effort of performing calculations with conventional DFT approaches is still non negligible and scales with the cube of the number of atoms. A recent optimised implementation of DFT was however shown to scale linearly with the number of atoms (ONETEP), and opened the route to large scale DFT calculations for molecules and nano-structures. Nonetheless, one bottleneck of DFT and ONETEP, is that it fails at describing well some of the compounds where strong correlations are present, in particular because the computational scheme has to capture both the band-like character of the uncorrelated part of the compound and the Mott-like features emerging from the local strongly correlated centres. A recent progress has been made in this direction by the dynamical mean-field theory (DMFT), that allows to describe the two limits (metal and insulator) in a remarkable precise way when combined with DFT. The ONETEP+DMFT implementation and strategies to overcome the main bottlenecks of this type of calculations will be discussed, and its applications illustrated by a few case of studies, such as the role of quantum entanglement in Myoglobin and heme systems. [more]

Disputation

7825 1480503600

Krishna Murari - Few-cycle high-energy mid-infrared pulse from Ho:YLF laser

[more]

Hamburg Photon Science Colloquium

7538 1479396933

Horst Weller - Nanocrystals in materials and life science applications

Nanocrystals are already used for many applications in technical products for everyday life. The talk will describe actual developments such as quantum dots in display and lighting technology, ultra-hard nanocomposite materials and materials for the visualization of biological events or malignant cells or tissues. Different chemical approaches and factors determining the biological response on fully synthetic nanocrystals will be reported. We will present approaches to improve targeting specificity and concepts to optimize physical proper ties to increase the sensitivity for imaging. [more]

MPSD Seminar

7760 1479991416

Matteo Lucchini - Attosecond dynamics in polycrystalline diamond

The possibility to manipulate the electrical properties of matter with very short opticalpulses is a fascinating field of research with possible far reaching applications inmany relevant technological fields. The first step towards the realization of this goal is to understand the ultrafast dynamics at the basis of light-matter interaction. Short and intense pulses allowed us to investigate a very interesting regime where the photon energy becomes comparable to the cycle-averaged kinetic energy of the electrons in the field. As the optical response of the material transitions from a classical to quantum-mechanical description many intriguing effects co-exist in this regime and the importance of inter- versus intra-band transitions is still debated. We used attosecond transient absorption spectroscopy (ATAS) to study the optical response of polycrystalline diamond driven by few-femtosecond, intense (IIR ~1012 W/cm2) infrared (IR) pulses. We monitored the system response by looking at the induced change in the absorbance with a 250-as pulse centred around 40 eV. We observed the appearance of oscillating features which modulate at twice the IR frequency, ωIR, and fully recover after the interaction. Simultaneous photoelectron acquisition from a gas nozzle placed in front of the diamond target allowed us to study the phase relation of the oscillating features and the pumping IR field. We found that the timing of the diamond response changes significantly with the probing energy and does not always follow the IR field adiabatically. Ab initio calculations performed by coupling time-dependent density functional theory (TDDFT) in real time with Maxwell’s equations reproduced the experimental observations. Further comparison with a numerical two-band model allowed us to conclude that intra-band motion dominates over inter-band transitions, thus identifying the dynamical Franz- Keldysh effect as the dominant mechanism in this regime. Our analysis constitutes an important step towards a full understanding of the optical properties of dielectrics in the Petahertz regime. [more]

CFEL Molecular Physics Seminar

7660 1479370995

Samuel Leutwyler - Cytosines: Excited-State Lifetimes, Nonradiative Decay Mechanism and Water Clusters

Photophysical investigations of the canonical nucleobases that make up DNA and RNA show that in room-temperature solvents, their excited states decay with (sub)picosecond lifetimes (τ = 0.3–2 ps). The apparent generality of ultrafast excited-state deactivation in the canonical nucleobases has led to the hypothesis that nucleobases are molecular survivors of the harsh UV environment on the early Earth before the emergence of life. [more]

CFEL Theory Seminar

7702 1479395160

Ulrich Schollwöck - Disentangling strongly correlated Quantum Systems

Strongly correlated quantum systems, where more traditional methods of quantum many-body physics fail, have attracted enormous attention over the last decades but still provide formidable problems for our understanding: High-Tc superconductors, frustrated quantum magnets, transition metal oxide and rear earth materials, ultracold atomic gases in optical lattices. Key numerical advances have been made using so-called tensor network methods, the best known of which is the density matrix renormalization group (DMRG). After an introduction into the methodology, I want to presentselected results from areas which in my view present particularly interesting challenges also in the future: non-equilibrium dynamics of correlated systems (here: ultracold atoms in lattices) and material properties of threedimensionaltransition metal oxides. [more]

MPSD Seminar

7683 1479296282

Sergey Brener - Some aspects of intrinsic electron-photon interaction in black phosphorus

Flexural and in-plane thermal fluctuations in crystalline membranes affect the band structure of the carriers, which has an effect on transport properties as well as carrier density of states of 2D systems. I consider a specific example of one-layer black phosphorus, which is a highly anisotropic material, and present our recent results on intrinsic carrier mobility. In contrast to graphene, where the mobility is determined by two-phonon (flexural) scattering, in black phosphorus one-phonon (in-plane) processes dominate. I also will show the results on DOS tail for holes in black phosphorus that have quasi-one-dimensional dispersion (my /mx » 1) and, as a result, an enhanced Van Hove singularity at the valence band top. Interaction with flexural phonons results in smearing of this singularity and to an appearing of a tail in DOS in the gap. The material parameters are determined by ab initio GW calculations and then are used for quantitative estimation of the above-mentioned effects. [more]

IMPRS-UFAST focus course

7684 1479305986

Experimental methods in materials research

This course will provide an overview of selected techniques used to probe the microscopic properties of condensed matter. The course will cover the use of these methods at steady state as well as their extension to transient measurements of non-equilibrium phenomena in condensed matter. [more]

Hamburg Photon Science Colloquium

6704 1479370972

Kerry Vahala - Towards integrated optical clocks & frequency comb spectroscopy systems

Like a tuning fork for light, optical resonators have a characteristic set of frequencies at which it is possible to confine light waves. At these frequencies, optical energy can be efficiently stored for lengths of time characterized by the resonator Q factor, roughly the storage time in cycles of oscillation. In the past there has been remarkable progress in boosting optical storage time in micro and millimeter-scale optical resonators with Q factors exceeding 100 billion. This opens up new opportunities to access a wide range of nonlinear phenomena and to create laser devices operating at low power. After reviewing the nonlinear physics of these devices, current efforts to miniaturize time standards and stable frequency sources for metrology and spectroscopy will be described. [more]

CFEL Molecular Physics Seminar

7659 1479370954

Bernd Winter - Electronic structure of aqueous solutions from liquid-jet soft-X-ray photoelectron and autoionization spectroscopy

Soft-X-ray photoelectron spectroscopy from liquid microjets has considerably contributed to an understanding of the electronic structure of aqueous solutions. Quantities that can be obtained include valence and core-level electron binding energies of both water solvent and atomic as well as molecular solutes. [more]

IMPRS-UFAST core course

7690 1479909142

Non-linear optics

The course provides an overview of the working principles of nonlinear optics with a focus on the basic physical concepts. We start from introducing relevant topics in linear optics (e.g., Maxwell equation, Lorentz model, Crystal optics, Optical pulse and dispersion), and continue to discuss key concepts in nonlinear optics such as phase matching and quasi phase matching, second-order nonlinear effects, and third-order nonlinear effects. [more]

Symposium

4340 1478859568

Frontiers in Physical Sciences

This symposium aims to enhance scientific cooperation between scientists from Argentina, Latin America and Max Planck Institutes. It is jointly organized by the International Center for Advanced Studies (ICAS) and the Max Planck Liason Office for Latin America, in cooperation with the Kolleg Programme of the Alexander von Humboldt Foundation. [more]

Hamburg Photon Science Colloquium

6703 1477059273

Faster than a Cycle of Light

Watching a single molecule move on its intrinsic time scale has been a dream of modern nanoscience. We show how a single oscillation cycle of phase-stable infrared pulses can accelerate and recollide electrons in solids. By combining this idea with sub-angstrom spatial resolution of scanning tunnelling microscopy we manage to control the ultrafast quantum motion of individual electrons in a single orbital of one molecule. Such elementary quantum processes allow us to record first slow-motion movies of individual vibrating molecules. [more]

MPSD Seminar

7604 1478683829

Energy and Entropy Transfer in Natural and Handmade Systems

The talk will cover the resonance energy transfer in light-harvesting systems and entropy transfer in nanomechancial resonators.In the first part, I will present a classical formulation of the quantum multichromophoric theory of resonance energy transfer developed on the basis of classical electrodynamics. The theory allows for the identification of a variety of processes of different order in the interactions that contribute to the energy transfer in molecular aggregates with intracoupling in donors and acceptor chromophores. Enhanced rates in multichromophoric resonance energy transfer are shown to be well described by this theory. Specifically, in a coupling configuration between $N_A$ acceptors and $N_D$ donors, the theory correctly predicts an enhancement of the energy transfer rate dependent on the total number of donoracceptor pairs. As an example, the theory, applied to the transfer rate in light harvesting II, gives results in excellent agreement with experiment. Finally, it is explicitly shown that as long as linear response theory holds, the classical multichromophoric theory formally coincides with the quantum formulation.In the second part, I will present a sideband cooling strategy that incorporates (i) the dynamics induced by structured (non-Markovian) environments in the target and auxiliary systems and (ii) the optimally time-modulated interaction between them. For the context of cavity optomechanics, when non-Markovian dynamics are considered in the target system, ground state cooling is reached at much faster rates and at much lower phonon occupation number than previously reported. In contrast to similar current strategies, ground state cooling is reached here for coupling-strength rates that are experimentally accessible for the state-of-the-art implementations. After the ultrafast optimal-ground-state-cooling protocol is accomplished, an additional optimal control strategy is considered to maintain the phonon number as closer as possible to the one obtained in the cooling procedure. Contrary to the conventional expectation, when non-Markovian dynamics are considered in the auxiliary system, the efficiency of the cooling protocol is undermined. [more]

Symposium

7518 1477484338

CUI International Symposium 2016

CUI invites to its fourth International Symposium on Thursday, 10 November 2016, in the Center for Free Electron Laser Science. In honor of the winner of this year’s Hamburg Prize for Theoretical Physics the symposium will cover modern trends in condensed matter physics. The prize is worth 40 000 Euro and will be presented by the Joachim Herz Stiftung together with CUI to Russian physicist Mikhail Katsnelson. [more]

MPSD Seminar

7577 1478187167

Transport through strongly correlated systems described by density functional theory

In this talk I will describe the evolution of our understanding on how to describe transport through strongly correlated systems in the framework of density functional theory (DFT).A first indication that DFT might be useful to tackle this situation came with the realization that the Kondo plateau in the zero-bias conductance may already be captured at the level of standard Landauer theory combined with DFT. Later it has been shown how the description of Coulomb blockade in the zero-bias limit can be achieved within DFT. In a more recent development we have proposed a DFT formalism to describe electronic transport in the steady state which uses the density on the junction and the steady current as basic variables. In a finite window around zero bias, a one-to-one map is established between the basic variables and both local potential on as well as bias across the junction. The resulting Kohn-Sham system features two exchange-correlation (xc) potentials, a local xc potential and an xc contribution to the bias. For weakly coupled junctions the xc potentials exhibit steps in the density-current plane which are shown to be crucial to describe the Coulomb blockade diamonds.Finally, I will present a recent parametrization of the xc potentials for the single-impurity Anderson model which correctly incorporates both the Kondo and Coulomb blockade regimes, i.e., both zero and finite temperature. This parametrization allows for calculation of currents and differential conductances at arbitrary bias and temperature at negligible numerical cost but with the accuracy of sophisticated renormalization group methods. [more]

MPSD Seminar

7526 1477570339

Designer nanostructures for visible light

There exists a size difference between molecules and visible wavelengths. Nanofabrication techniques can be adopted to obtain designed meta-molecules or meta-materials, with interesting optical properties. [more]

Hamburg Photon Science Colloquium

6702 1477058965

Nanomembrane Devices: from Concepts to Applications

Nanomembranes are thin, flexible, transferable and can be assembled into 3D micro- and nanoarchitectures. This makes them attractive for a broad range of applications and scientific research fields ranging from strain-tunable heterostructure devices to ultra-compact 3D systems both on and off the chip. Rolled-up nanomembranes can be exploited to rigorously compact electronic circuitry, create novel optical components and open up pathways towards entirely new biomedical applications. [more]

MPSD Seminar

7561 1478081516

TDDFT in solids for electron dynamics induced by ultrashort laser pulses

Since 2000, we have been developing a real-time, real-space computationalmethod based on time-dependent density functional theory to describe electron dynamics in crystalline solids induced by light pulses. In a microscopic scale, we solve the time-dependent Kohn-Sham equation in a unit cell of solid treating the applied electric field is by the vector potential. We further combine the microscopic calculation with the dynamics of light electromagnetic field in a multiscale modeling, as describe in the figure. In my presentation, I first explain our method including some historical aspects. Then I will show some recent and on-going applications such as energy transfer from a femtosecond laser pulse to electrons in quartz and graphite, and ultrafast changes of dielectric properties of diamond by an intense laser pulse. [more]

MPSD Seminar

7529 1477580346

Designing Excitons in van der Waals Heterostructures

Van der Waals heterostructures (vdWHs) represent a novel and largely unexplored class of materials. Since 2013, when Geim and Grigorieva first conceived the stacking of 2D (two-dimensional) materials to create artificial layered structures with tailored properties, a number of promising (opto)electronics devices, e.g. light emitting diodes, solar cells, ultra-fast photodetectors, transistors etc. have been successfully fabricated. It is well established that for isolated 2D semiconductors and vdWHs the optical response is governed by excitonic effects. A theoretical understanding of excitonic effects and of how the electronic screening is affected for the more complex case of multi-layer structures is still lacking due to the computational limitations of standard ab-initio methods. [more]

Tagung

4322 1474978850

20. Deutsche Physikerinnentagung

Die jährliche Deutsche Physikerinnentagung wird von der Deutschen Physikalischen Gesellschaft (DPG) und ihrem Arbeitskreis Chancengleichheit veranstaltet. Dabei bekommen Physikerinnen aus allen Bereichen und Karrierestufen die Chance sich miteinander zu vernetzen und auszutauschen. Im Vordergrund steht dabei ein fächerübergreifender fachlicher Austausch, um einen Überblick aus allen Bereichen der Forschung und der Physik zu erhalten. Erfahrungsberichte aus dem Alltag verschiedener Berufe aus Industrie, Wirtschaft und Forschung geben einen Einblick über die vielfältigen Möglichkeiten von Physikerinnen und die Chance die Arbeitsituationen von Physikerinnen zu diskutieren.Zudem diskutieren wir in diesem Jahr in der Podiumsdiskussion die Ziele, die Umsetzung und was tatsächlich mit Frauenförderungsprogrammen erreicht wird. [more]

CFEL Theory Seminar

7525 1477569806

Nonlinear optical spectroscopy with nonclassical light, photon counting detection and extreme wavelengths techniques

The progress in quantum optics utilizes a unique photon state configuration for engineering of the ultimate light-matter interactions with relatively simple material systems. It results in a broad range of photonic applications including radiation sources, quantum communication, information, computing and nanotechnology. The development of the ultrafast multidimensional nonlinear spectroscopy that has been enabled by progress in ultrafast optical technology provides a unique tool for probing complex molecules, semiconductors, nanomaterials by classical light fields. [more]

Symposium

6711 1477486146

Second Q-MAC Symposium

The second symposium of the ERC Synergy Grant Q-MAC (Frontiers in Quantum Materials’ Control) takes place at the Venice International University, Isola di San Servolo in Venice, Italy. [more]

Disputation

7490 1480509809

In-liquid Electron Microscopy and Diffraction for real-time observation and structural analysis

[more]

Hamburg Photon Science Colloquium

6701 1474965361

Model systems in heterogeneous catalysis at the atomic scale

Our understanding of heterogeneous catalysis is to a large extent based on the investigation of metal single crystals as models. Increasing the complexity of the models, resembling a real disperse metal catalyst, allows one to catch some of the complexity that cannot be covered by metal single crystals alone. We have developed model systems based on metal deposits on single crystalline oxide films, which may be studied at the atomic level using the tools of surface science. [more]

Disputation

6865 1476260541

Nonlinear phononics and structural control of strongly correlated materials

[more]

Disputation

6822 1480500957

Jhih-An You - Light-induced Electronic Hole Dynamics and its Application

[more]

MPSD Seminar

7364 1476715756

Adventures in XFEL data analysis

This talk will showcase algorithms that I have developed over the course of my PhD suited to X-ray free electron laser data processing. At present, generating merged datasets to sub-atomic resolution can be tricky at LCLS due to the limitations of the photon energy and detector distance. I will present some of the challenges faced by processing diffraction patterns, collected at LCLS, to generate a 1.15 Å resolution dataset, and how these new algorithms have proved useful to solve them. [more]

Tagung

6823 1476096845

PIER Graduate Week 2016

Welcome to the PIER Graduate Week 2016, an interdisciplinary lecture and workshop week for PhD students. The PIER Graduate Week offers a wide range of introductory and focus courses in the PIER research fields of Particle & Astroparticle Physics, Nanoscience, Photon Science, Infection & Structural Biology. It aims at PhD students, MSc students, postdoctoral researchers and other interested scientists. [more]

MPSD Seminar

6736 1475074382

Optical Materials Design of Transition-Metal Dichalcogenides and Frustrated Mott Insulators

Spurred by recent progress in melting, enhancement and induction of electronic order out of equilibrium, a tantalizing prospect concerns instead accessing transient Floquet steady states via broad pump pulses, to affect electronic properties. [more]

CFEL Theory Seminar

6735 1475074044

Inflated nodes and surface states of topological superconductors

The new paradigm of topology in condensed matter physics does not only pertain to insulators and semimetals but also to superconductors. Topological superconductors are predicted to show many novel physical properties. [more]

Informationsveranstaltung

6646 1474367639

Forschen in Europa: Nationale und europäische Forschungsförderung

Mit der kostenlosen Veranstaltung „Forschen in Europa: Nationale und europäische Forschungsförderung“ wollen die Kooperationsstelle EU der Wissenschaftsorganisationen (KoWi) und die Universität Hamburg Graduierte, Doktoranden/innen, Postdoktoranden/innen und Nachwuchsgruppen über die vielfältigen nationalen und europäischen Unterstützungsmöglichkeiten informieren. [more]

MPSD Seminar

6712 1474980087

Ultracold Fermions in Optical Lattices as a Testbed for Dynamically Driven Complex Materials

Complex quantum many-body systems are ubiquitous in nature, but their behaviour often remains very challenging to predict with analytical or numerical calculations - especially when it comes to dynamics. However, using ultracold atoms in optical lattices it is possible to create precisely tunable, yet very accessible artificial solids, which can be probed with a large arsenal of observables. Using this experimental set-up, we demonstrate how a periodically modulated lattice can be described by an effective Floquet-Hamiltonian on longer time scales - even when driving the system far from equilibrium. This allows for implementing Haldane's model for a topological insulator, and mapping out its topological transitions, by applying an oscillating force to a honeycomb lattice. Using an oscillating magnetic field gradient, we also engineer spin-dependent bands. By adding interactions to the optical lattice system, we create a pure realisation of the Hubbard model and study how the distribution of anti-ferromagnetic correlations therein depends on the geometry of the lattice. We investigate how fast correlations can re-arrange, by deforming the lattice geometry on time-scales ranging from the sudden to the adiabatic regime. Finally, we explore how an oscillating force applied to this interacting system may be used to tune and enhance the magnetic exchange energy beyond the regimes accessible within the Hubbard model. [more]

MPSD Seminar

6692 1474640231

Dynamical phase transitions in the long-range (powerlaw) interacting transverse-field Ising model

Dynamical phase transitions (DPTs) have gained a lot of interest in the past few years in a variety of quantum many-body systems, where a system in its groundstate is quenched by abruptly changing a control parameter of the Hamiltonian, such as interaction strength or external field. Afterwards, a DPT can be detected in one of at least two forms: a type-I DPT which is detected, after relaxation in time, through the nonanalyticity of an appropriate order parameter as a function of the control parameter through which the quench is effected; and a type-II DPT which is detected as a nonanalyticity of the Loschmidt echo return rate as a function in time, without giving care as to whether or not a stationary state has been reached in the time evolution. [more]

MPSD Seminar

6659 1474457740

Collective dynamics in quantum emitter systems

Time evolution in ensembles of quantum emitters (atoms, molecules, ions, Rydberg atoms, quantum dots etc) at low vs. high densities is fundamentally different. As particles get closer together, strong environment-mediated interactions start playing an important role both in the coherent (such as dipole-dipole interactions) as well as in the incoherent evolution (super- /subradiance). [more]

Disputation

6632 1474277373

Nonequilibrium ultrafast excited state dynamics in DNA

[more]

MPSD Seminar

6610 1473947932

Correlations in the zone: ultrafast electronic dynamics and vibrational symmetry breaking in quantum materials

The physics of the “ultra-fast” and “ultra-small” are often closely linked, motivating experiments that access these extremes. In this talk, I will discuss the application of ultrashort light pulses, from THz to X-rays, to the study of dynamics and emergent correlations in quantum materials. [more]

CFEL Theory Seminar

6636 1474289720

Exploring molecular strong field ionization with ahybrid coupled channels approach

Molecular strong field ionization (SFI)is at the heart of several ultrafast imaging/spectroscopic techniques such aslaser induced electron diffraction and high harmonic spectroscopy. Whileproof-of-principle experiments are underway, it is still a long way before theycan evolve into a standard imaging techniques. The coupled motion of electronsand nuclei under the influence of a non-perturbative external laser field isnot fully understood yet and there is a strong demand for developing many bodymethods that can model these molecular SFI based processes. [more]

MPSD Seminar

6578 1473778885

Light-matter interaction: from weak to strong coupling

When an exciton transition and a resonant optical mode exchange energy faster than any competing dissipation process, it can lead to light-matter strong coupling. This brings about interesting properties possessed by neither the original exciton nor the optical mode and leads to new possibilities such as enhanced conductivity of organic semiconductors. In this case, the enhancement stems from the delocalized nature of the hybrid states over the spatial extent of the optical mode which is also expected to affect energy transport according to recent theoretical studies. [more]

Tag des Wissens

6318 1471948331

Tag des Wissens "Life Science"

Was passiert im Inneren von Zellen? Wie funktioniert der hellste Röntgenlaser der Welt und wie kommen Rechtsmediziner Verbrechern auf die Spur? Der erste Tag des Wissens gibt Einblicke in aktuelle Forschungsthemen. [more]

MPSD Seminar

6342 1472806240

Memcomputing: a brain-inspired topological computing paradigm

Which features make the brain such a powerful and energy-efficient computing machine? Can we reproduce them in the solid state, and if so, what type of computing paradigm would we obtain? [more]

MPSD Seminar

6341 1471948242

The Particle-Hole Map: a Computational Tool to Visualize Electronic Excitations

The particle-hole map (PHM) is a new visualization tool to analyze electronic excitations in molecules in the time- or frequency domain, to be used in conjunction with TDDFT or other ab initio methods [1–3]. The purpose of the PHM is to give detailed insight into electronic excitation processes which is not obtainable from local visualization methods such as transition densities, density differences, or natural transition orbitals. The PHM provides information on the origins, destinations, and coherences of charge fluctuations during an excitation process. In contrast with the transition density matrix, the PHM has a statistical interpretation involving joint probabilities of individual states and their transitions, and it is easier to read and interpret. [more]

Faraday Discussion

5733 1465388963

Ultrafast Imaging of Photochemical Dynamics

Photochemical reactions have tremendous scientific importance, ranging from photosynthesis to atmospheric reactions, and technologies such as sensors or displays. Due to the intrinsic complexity of photochemical reactions, they remain the least understood type of chemical process. Nonadiabatic dynamics, ultrafast time-scales, quantum effects and conical intersections are known to be important, but a detailed comprehension remains elusive. However, new experimental techniques capable of monitoring photochemical processes in unprecedented detail are appearing. This includes the development of intense-laser techniques, the construction of free-electron lasers such as the XFEL in Europe and the LCLS in the USA, new sources of pulsed electrons, advanced detection techniques, and important advances in theoretical modelling of quantum dynamics. Many of these techniques are developed by research communities not traditionally concerned with photochemistry, but provide an opportunity to shed new light on photochemical dynamics. [more]

MPSD Seminar

6278 1470062336

Light induced enhancement of superconductivity via melting of competing bond-density wave order in underdoped cuprates

We develop a theory for light-induced superconductivity in underdoped cuprates in which the competing bond-density wave order is suppressed by driving phonons with light. Close to a bond-density wave instability in a system with a small Fermi surface, such as a fractionalized Fermi liquid, we show that the coupling of electrons to phonons is strongly enhanced at the bond-density wave ordering wavevectors, leading to a strong softening of phonons at these wavevectors. For a model of classical phonons with anharmonic couplings, we show that thecombination of strong softening and driving can lead to large phonon oscillations. When coupled to a phenomenological model describing the competition between bond-density wave order and superconductivity, these phonon oscillations melt bond-density wave order, thereby enhancing pairing correlations. [more]

MPSD Seminar

6244 1469455014

Early charge separation events in light-harvesting materials

The photoinduced charge-separation events occurring in photovoltaic and light harvesting systems have traditionally been interpreted in terms of the incoherent kinetics of optical excitations and of charge hopping. Although signatures of quantum coherence were recently observed in energy transfer in photosynthetic bacteria andalgae[1] still very little is known about the role of quantum coherence at room temperature in technologically relevant organic photovoltaic materials. Recent experiments found evidence for an ultrafast long-range charge separation in such systems but could not differentiate between coherent and incoherent charge-transfermodels.[2] [more]

MPSD Seminar

6245 1469455848

Growth and electronic structure of single-layered transition metal dichalcogenides

The discovery of graphene established the possibility of obtaining stable two-dimensional solids, and it was soon realized that layered materials other than graphite can be used as bulk parents for novel two-dimensional materials. Among them, layered transition metal dichalcogenides have attracted considerable attention due to interesting physical properties and potential for electronics applications. While most of the research focused on mechanically exfoliated specimens, many proposed approaches to characterizing these materials, as well as potential applications, require large-area and high-quality samples. These can be achieved by epitaxial growth methods developed in our group. [more]

Disputation

6240 1469437130

An atomic perspective of the photodissociation and geminate recombination of triiodide in condensed phases

[more]

MPSD Seminar

6224 1469094355

Chemistry under Strong Coupling

Light-matter interactions have been extensively studied by physicist in quantum optics and condensed matter physics, [1] but there are only fewer attempts to understand this effect in molecular science. [2, 3] [more]

MPSD Seminar

6225 1469103630

Dynamics of the Transverse Field Ising Chain after a Sudden Quench

Due to experimental advances in the preparation and control of ultra-cold atomic gases, there is a widespread interest in the behaviour of quantum systems out of equilibrium. A common way to probe quantum systems for non-equilibrium phenomena is given by sudden quenches. [more]

Hamburg Photon Science Colloquium

5234 1462794390

It's All About Water

Ultrafast vibrational spectroscopy can tell a lot about molecular dynamics. Quite diverse examples will be discussed, highlighting the importance of water as a very special substance: the ultrafast dynamics of bulk water and concentrated salt solution studied by THz photon echo spectroscopy, the catalytic cycle of an artificial photosynthetic system for light-driven water splitting, and the response of an allosteric protein whose dynamics is dictated by the water solvation layer. [more]

Disputation

5929 1480500853

Nele Müller - Electron diffraction and controlled molecules

[more]

Disputation

5880 1480499955

Generation and control of super-octave-spanning spectra

[more]

Hamburg Photon Science Colloquium

5237 1464259684

Plasmon-Enhanced Raman Scattering

Plasmons are the collective excitations of free electrons. They focus light into nanoscale volumes, increasing electromagnetic fields by orders of magnitude. Plasmonic enhancement in light scattering (SERS) leads to a 10⁸ increase in the cross section. I will present Raman measurements on graphene and nanotubes coupled to nanoplasmons. The enhancement will be described as a higher-order Raman process with striking consequences for our understanding of plasmon-matter interaction at the nanoscale. [more]

CFEL Sommerfest

5928 1466759717

CFEL Sommerfest

Join us at the CFEL Sommerfest! CFELians, partners and kids are more than welcome! [more]

MPSD Seminar

5999 1467371002

Electronic and Structural Dynamics in Solids: A Momentum-Resolved View on Microscopic Coupling and Correlation Phenomena

The coupling and mutual dependence of electronic and vibrational degrees of freedom is at the heart of microscopic as well as macroscopic phenomena in condensed matter. Ultrafast pump-probe techniques provide experimental access to these coupling and correlation effects by revealing the response of electrons and lattice to specific excitation of a material. [more]

CFEL Theory Seminar

5927 1466690975

Nonequilibrium dynamics of strongly coupled phonon-mediated superconductors

Recent developments in ultra-fast laser techniques allow experimentalists to reveal intriguing aspects of the dynamics of superconductors such as the Higgs oscillations (amplitude oscillations of the order parameter) and photo-induced superconductivity. These experiments demonstrate the interesting possibility of manipulating superconductivity in nonequilibrium settings. However, the properties of nonequilibrium superconductors are not fully understood, and further theoretical explorations are needed. [more]

MPSD Seminar

5731 1465378311

Coupled Cluster Theory for Strong Correlations

Coupled cluster theory is the dominant method in wave function-based calculations in systems of small to moderate size. It provides exceptionally accurate predictions for a wide array of energetics and properties. Moreover, it is size extensive, meaning that it can fruitfully be applied to condensed systems, provided only that one has computational resources sufficient for the task. Unfortunately, coupled cluster theory often breaks down in the presence of strong correlations, such as those responsible for superconductivity or various magnetically-ordered states. [more]

Hamburg Photon Science Colloquium

5242 1465300092

Testing Fundamental Physics with Cold Atoms and Molecules

Cold and ultracold molecules provide a sensitive way to search for new physics, e.g. variation of fundamental constants, dark energy, or new elementary particles. I will describe some of these ideas, with particular emphasis on the search for a permanent electric dipole moment of the electron, which already provides a strong constraint on possible supersymmetric theories of particle physics. Laser cooling can now be applied to molecules. I will discuss the recent advances in that area and the extraordinary sensitivity that this new approach can bring to tests of fundamental physics. [more]

MPSD Seminar

5933 1466970174

Time-dependent quantum transport in nanosystems: A nonequilibrium Green's function approach

Quantum transport is often discussed in the steady-state regime where the characteristics of the system are described in terms of the energy-dependent transmission or conductance. There is, however, no guarantee that this description would capture the essential physics in, say, atomic-scale junction operating at high frequencies. Therefore, we look for an accurate theory for describing the full time-dependence. The time-dependence also provides us with ''transient spectroscopy'' which can give detailed information about the nanosystems out of equilibrium. [more]

CFEL Theory Seminar

5887 1466506644

Making Majoranas talk to charge

In this talk, I will first give an introduction to Majorana bound states (MBS), zero-energy modes predicted to appear in exotic spin-polarized p-wave superconductors. MBS satisfy non-Abelian statistics and, in addition, encode quantum information in a topologically protected manner, which makes them highly interesting for quantum computation applications. The required p-wave superconductivity seems to be hard to find in nature, but recent theoretical works have shown that it can instead be artificially engineered, for example in a semiconductor nanowire with strong spin-orbit coupling which is covered by a superconductor and exposed to a magnetic field. I will also discuss the recent experimental progress towards creating and detecting MBS. [more]

Hamburg Photon Science Colloquium

5241 1462794235

Networked Quantum Information Technologies

Hybrid light-matter networks offer the promise for delivering robust quantum information processing technologies, from sensor arrays to secure communications to quantum simulators and eventually to a quantum computer. Photonics plays a major role in delivering these new enhanced performance applications. I will describe recent science and engineering progress towards build a resilient, scalable photonic quantum network. [more]

MPSD Seminar

5735 1465896704

Revealing Hidden Phases in Correlated Electron Systems using Nonlinear Optics

The iridium oxide family of correlated electron systems is predicted to host a variety of exotic electronic phases owing to a unique interplay of strong electron-electron interactions and spin-orbit coupling. There is particular interest in the perovskite iridate Sr₂IrO₄ due to its striking structural and electronic similarities to the parent compound of high-Tc cuprates La₂CuO₄. Recent observations of Fermi arcs with a pseudogap behavior in doped Sr₂IrO₄ and the emergence of a d-wave gap at low temperatures further strengthen their phenomenological parallels. [more]

Hamburg Photon Science Colloquium

5235 1462794350

Ultrafast Electron Kinetics in Graphene

Graphene is an ideal material to study new processes in the ultrafast carrier kinetics of a two-dimensional system: Its linear energy dispersion and the vanishing bandgap allow new and surpising electron scattering processes, suppressed in conventional semiconductors: A typical, fascinating example is a process which generates two optically excited electrons out of one photon. [more]

MPSD Seminar

5736 1465390831

Growth of YBa₂Cu₃O₇-films for device applications

The high-temperature superconductor YBa₂Cu₃O₇ is a very interesting material for many device applications ranging from wiring for energy transmission and high field magnets to superconducting filters and high frequency electronics in the THz regime. [more]

CFEL Molecular Physics Seminar

5842 1465829098

Theoretical Spectroscopy of Complex Chemical Systems

Quantum-chemical calculations are essential for the assignment and interpretation of spectra of small molecules as well as complex molecular systems. Large molecular systems present a significant challenge not only because of the increasing computational effort that is required for an accurate quantum-chemical description, but also require new approaches for the interpretation of the large amount of data provided by such calculations. On the other hand, small molecular systems with a complicated electronic structure, such as transition metal complexes, pose additional challenges and their theoretical spectroscopy also requires novel quantum-chemical approaches. [more]

MPSD Seminar

5730 1465378172

Nonequilibrium Study of Competing Orders

Competition between ordered phases, and their associated phase transitions, are significant in the study of strongly correlated systems. [more]

MPSD Seminar

5737 1465391379

Collective modes of the electron-hole condensate in the (putative) excitonic insulator 1T-TiSe₂

TiSe₂ is one of the simplest charge density wave (CDW) materials, forming a 2×2 superlattice below a transition temperature T_C = 200 K, but the origin of this phase is controversial. Its nearly inverted band structure led early authors to identify TiSe₂ as an “excitonic insulator,” which is an electronic instability involving spontaneous proliferation of excitons. The problem is that the CDW also exhibits a sizeable lattice distortion, leading later authors to identify it as a conventional Peierls phase. That said, an excitonic phase would also create an incidental lattice distortion, since the interaction with phonons can’t be switched off. The arguments on the matter have gone in circles for decades. [more]

Disputation

5713 1480500703

Metal Ion Based Probes for Imaging

[more]

 
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