Archiv 2017

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. [mehr]

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

MPSD Seminar
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]. [mehr]
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. [mehr]

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

MPSD ARD Seminar

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

MPSD Seminar
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. [mehr]

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

MPSD Seminar

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

MPSD Seminar

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

MPSD Seminar
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) [mehr]

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

MPSD ARD Seminar
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. [mehr]

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

MPSD ARD Seminar
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. [mehr]

Binghai Yan - Nonlinear optical responses of Weyl semimetal materials

MPSD Seminar
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. [mehr]
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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. [mehr]

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

MPSD Seminar
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Superconductivity - IMPRS-UFAST focus course

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 [mehr]

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

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

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

MPSD Seminar

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

MPSD Seminar
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Last steps of your PhD - Info meeting

Info meeting for PhD students on Bahrenfeld Campus
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. [mehr]

Michael Schüler: Nonequilibrium topological states traced by transient spectroscopies

MPSD Seminar
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. [mehr]
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Atomically Resolved Dynamics Group [mehr]

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

MPSD Seminar

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

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


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

MPSD Seminar
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). [mehr]
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IMPRS Job Seminar

IMPRS-UFAST skills course
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. [mehr]
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Basics of chemistry and biochemistry - IMPRS-UFAST core course

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. [mehr]

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

MPSD ARD Seminar
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. [mehr]
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Moderation training

IMPRS-UFAST skills course
Learn powerful and effective methods for conducting all types of meeting from an experienced expert. [mehr]

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

MPSD ARD Seminar
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. [mehr]
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Intermolecular interactions - IMPRS-UFAST focus course

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. [mehr]

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

MPSD Seminar
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. [mehr]

Lukas Müchler - Exploring topological phenomena in Molecules

MPSD Seminar
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. [mehr]

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

MPSD Seminar
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. [mehr]
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Frederike Ahr - High energy multi-cycle terahertz generation

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Science Slam Workshop (IMPRS-UFAST skills)

IMPRS-UFAST skills course
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! [mehr]
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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]. [mehr]

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

CFEL Molecular Physics Seminar
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. [mehr]

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

MPSD Seminar
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. [mehr]
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Abid Hussain - Theory and computation of time-resolved spectroscopies for systems in complex environments

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

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. [mehr]

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


Michael Lubasch - Density Functional and Tensor Network Theory

MPSD Seminar
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)." [mehr]

Yang Peng - Boundary Green functions of topological insulators and Superconductors

MPSD Seminar
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) [mehr]
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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. [mehr]
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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 to find the preliminary program and the online application form, which has to be submitted before February 22nd. [mehr]

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

MPSD Seminar
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. [mehr]
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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. [mehr]
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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 [mehr]
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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. [mehr]

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

MPSD Seminar
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. [mehr]

Jorge Jover - Open quantum systems: a geometric description

MPSD Seminar
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) [mehr]
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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. [mehr]
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Irene Dornmair - Advanced Beam Dynamics and Diagnostics Concepts for Laser-Plasma Accelerators


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

MPSD Seminar
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. [mehr]
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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. [mehr]
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Solid State Physics

IMPRS-UFAST core course
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. [mehr]

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

MPSD Seminar
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). [mehr]

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

MPSD Seminar
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. [mehr]

March for Science (non MPSD)

March for Science
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: and [mehr]
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Good scientific practice

IMPRS-UFAST skills course
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. [mehr]

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

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. [mehr]
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Julia Hengster - Towards ultrafast time-resolved experiments with nanoscale objects and surfaces


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

MPSD Seminar
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. [mehr]

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

MPSD Seminar
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. [mehr]

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

MPSD Seminar
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. [mehr]

Michael Lorke - Carrier dynamics in MoS2

MPSD Seminar
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. [mehr]

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

MPSD Seminar
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. [mehr]
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Tong Zhou - Quantum Spin-quantum Anomalous Hall Effect with Tunable Edge States in Sb Monolayer-based Materials

MPSD Seminar
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. [mehr]
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Kemal Shafak - Large-scale laser-microwave synchronization for attosecond photon science facilities

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Ultrafast techniques

IMPRS-UFAST core course
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. [mehr]
9275 1488977950

Introduction to C++ for PhD students

IMPRS-UFAST skills course
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. [mehr]
9128 1487771964

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

MPSD Seminar
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. [mehr]
9034 1487062128

Eliza Casandruc - Nonlinear Optical Control of Josephson Coupling in Cuprates


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

MPSD Seminar
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 [mehr]

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

MPSD Seminar
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. [mehr]
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. [mehr]

Yoni Toker: Watching Isolated Molecules Change Their Shape

CFEL Molecular Physics Seminar
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. [mehr]
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. [mehr]
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. [mehr]
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. [mehr]
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Source technology

IMPRS-UFAST core course
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. [mehr]
7739 1484145442

Preparing for your PhD defence

IMPRS-UFAST skills course
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. [mehr]

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

CFEL Theory Seminar
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. [mehr]

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

MPSD Seminar
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. [mehr]
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The theory of electronic structure and molecular dynamics

IMPRS-UFAST core course
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. [mehr]
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Matthias Bartelmann - A microscopic theory for cosmic structures

Hamburg Photon Science Colloquium
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. [mehr]

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


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

MPSD Seminar
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. [mehr]
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Getting tasks done

IMPRS-UFAST skills course
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. [mehr]
6708 1479908841

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

Hamburg Photon Science Colloquium
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. [mehr]
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Ultrafast spintronics with terahertz radiation

MPSD Seminar
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. [mehr]
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