Zeit | Sprecher & Vortragsthema |
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25.07.2023
Hybrid Zoom / CS B.30.23, R.3-1 |
Qigang Zhong On-surface molecular reactions studied by atomically precise imaging and manipulation Universität Gießen |
18.07.2023
Hybrid Zoom / CS B.30.23, R.3-1 |
Christian Ast Superconducting Quantum Interference at the Atomic Scale MPI-FKF Stuttgart |
23.06.2023
Hybrid Zoom / CN B.425 R.206 |
Pintu Das Topological Hall effect due to nanoscale magnetic skyrmions in ultra-thin film multilayers Indian Institute of Technology Delhi, New Delhi, India In the last decade, the Hall effect family has been enriched by a new type, called Topological Hall effect (THE) which describes a contribution to transverse current that is not usually covered in the ordinary or anomalous Hall effect (AHE). Whereas AHE result from spin orbit interaction, the THE is a manifestation of exchange interaction of the spin of the carriers with the underlying magnetic textures. Recent experimental and theoretical investigations suggest that a magnetic skyrmion or a skyrmion lattice possessing a nonzero topological charge (topologically nontrivial spin texture) may result in THE. In this talk, I will discuss the results of THE observed in the skyrmion phase for Pt|Al|Co|Pt based ultra- thin film multilayer stacks. Other than observing a correlation with the evolution of skyrmion in the system, our analysis suggests undetected skyrmions resulting in a large THE comparable with the value observed for the skyrmions which are detected by magnetic force microscopy. Our electrical fluctuation experiments indicate an increase in fluctuations as a skyrmion phase evolves in the system. I will discuss the possible scenarios to understand our experimental data. |
20.06.2023
Hybrid Zoom / CS B.30.23, R.3-1 |
Maximilian Kristen Noise and dissipation in superconducting granular aluminum circuits Physikalisches Institut des KIT |
13.06.2023
Hybrid Zoom / CS B.30.23, R.3-1 |
Felix Lüpke Quantum states in van der Waals heterostructures studied by Scanning Tunneling Microscopy Peter-Grünberg-Institut, Forschungszentrum Jülich |
06.06.2023
Hybrid Zoom / CS B.30.23, R.3-1 |
Maximilian Pallmann Purcell-enhanced emission and collective effects of NV centers in diamond coupled to a microcavity Physikalisches Institut, KIT |
25.05.2023
Hybrid Zoom / CS B.30.23, R.3-1 |
Katharina Kaiser Charging dynamics of single molecules in STM CNRS – IPCMS, Straßburg, Frankreich |
09.05.2023
Hybrid Zoom / CN B.425 R.206 / CS B.30.23, R.3-1 |
Wolfgang Pfaff Plug & Play Quantum Circuits University of Illinois at Urbana-Champaign Superconducting quantum circuits are a leading platform for building large-scale quantum systems, such as quantum processors or simulators, from the bottom up. Circuit quantum electrody-
namics provides us with excellent control over single artificial atoms, microwave photons, and
their interactions. Scaling circuits to larger and larger numbers of qubits, however, is an ongoing
challenge: Owing to inevitable imperfections in designing and fabricating devices, building large
systems with precisely defined interactions is very difficult. |
25.04.2023
Zoom |
Nils Marquardt Enlightening spin triplet superconductivity in UTe2 CEA Grenoble |
08.03.2023
Hybrid Zoom / CN B.425 R.206 |
Hugo Perrin, Thibault Scoquart Simulation of superconductivity on an IBM quantum computer using error mitigation protocols TKM KIT We perform digital simulations of nonequilibrium dynamics of a small superconductor on an IBM quantum computer. With the toy model realized on three qubits, we discuss various error-mitigation protocols that allow us to improve the simulation results. In particular, we have developed and benchmarked a new approach that turns the cross-talk effects into depolarizing noise channel using randomized compiling. |
03.03.2023
Hybrid Zoom / CN B.425 R.206 |
Dmitry Reznik Observing quantum materials in real time by pump-probe Raman scattering Department of Physics, University of Colorado - Boulder Pump-probe experiments open a completely new way to study and control quantum materials. Their behavior away from thermal equilibrium, generation of metastable phases, photoexcited states, quantum computing-related phenomena, chemical reactions, energy dissipation, etc. can now be measured in real time with unprecedented precision due to rapid advances in ultrafast lasers and x-ray sources. In this talk I describe the time-resolved Raman scattering lab at the University of Colorado. It shares an ultrafast laser system with an angle-resolved photoemission (ARPES) setup, which allows investigation of bosonic and fermionic excitations under the same driven nonequilibrium conditions. I will discuss new physics that was uncovered using time-resolved Raman in three projects completed at the University of Colorado. The first one combined the two techniques to directly follow electron-hole excitations as well as the increase in the population of the Raman-active G-phonon in graphite after an excitation by an intense laser pulse. This work uncovered a new relaxation pathway later confirmed by others: The energy is first transferred to optical phonons near the zone boundary K-points, which then decay into G-phonons via phonon-phonon scattering. This work showed that phonon-phonon interactions must be included in any calculations of hot carrier relaxation in optical absorbers even for short timescales. I will then switch gears to a prototypical copper oxide superconductor YBa2Cu3O6+x. First, I will present our results on ultrafast magnetic dynamics where we followed time-evolution of the two-magnon Raman scattering in an insulating antiferromagnetic sample. Then I will discuss nonequilibrium dynamics of the apical oxygen phonon as a new window into electronic states and electron-phonon coupling. |
22.02.2023
Hybrid Zoom / CN B.425 R.206 |
Jeremy Sourd Superconductivity and Kondo lattice effects in La1-xCexFeSiH:
An interdisciplinary approach to a strongly correlated electron system Laboratoire Ondes et Matière d'Aquitaine, Institut de Chimie de la Matière Condensée de Bordeaux, University of Bordeaux, France Strongly correlated electron systems refer to a broad class of materials in which exotic phases of matter such as
unconventional superconductivity are observed. Very often, the strong electronic correlation is associated with atomic Coulomb repulsion in localized d or f orbitals.
My PhD thesis [1] was the occasion for an interdisciplinary work between solid state chemistry and theoretical
physics. Starting from the iron based superconductor LaFeSiH, we studied the family of intermetallic hydrides La1-xCexFeSiH (0 ≤ x ≤ 1), in which rich physical properties might emerge from the interaction between cerium 4f and
iron 3d electrons.
On one side, we realized the synthesis of those compounds, together with structural analysis. The physical
properties measurements permits to identify superconductivity, incoherent Kondo effect and coherent Kondo
lattice regime. Furthermore, we used a systematic methodology to extract phenomenologically some
temperature scales and plot a phase diagram temperature vs cerium concentration x [2].
On the other side, we studied some effective model Hamiltonians adapted to the correlated electrons present in
those compounds. In particular, we considered a non-local Kondo hybridization between the cerium 4f orbital and the iron 3d orbital. We showed that this non local hybridization leads to a pocket selective doping effect of iron by cerium, related to the symmetry of the cerium low energy crystal field Kramers doublet. We also proposed some experimental signatures of this effect through light-matter experiments, namely ARPES, optical conductivity and Raman spectra [3]. |
15.02.2023
Hybrid Zoom / CN B.425 R.206 |
Ina Schäfer Quantum Informatics - From Quantum Gates to Quantum Software Engineering KIT, Institut für Informationssicherheit und Verlässlichkeit (KASTEL) While quantum computing hardware is becoming more and more available, the demand for quantum software is also increasing. As in classical computing, the expectation is that after quantum computing hardware has reached a certain maturity, the main value creation in quantum computing will be obtained from quantum software. In order to facilitate the use of quantum computing to solve industrial-scale applications, advances in quantum informatics, and especially in quantum software engineering are needed. In this presentation, I will explore the relationship between quantum computing and classical software engineering by focussing on three main aspects. First, I will show what can be learnt from classical programming language and compiler technology for the implementation of quantum programming languages. Second, for scaling the development of quantum programs, I will present first results on design patterns for quantum programming. Third, in order to ensure correctness of quantum programs, I will focus on verification techniques and correctness-by-construction development for quantum programs. |
14.02.2023
Hybrid Zoom / CS B.30.23, R.3-1 |
Oliver Gröning Exploiting the chirality of the intermetallic compound PdGa on its surfaces Eidgenössische Materialprüfungs- und Forschungsanstalt (Empa), Materials Science and Technology The chirality of biomolecules is a key structural property for determining their physiological activity. A prominent example is the difference in taste between R-limonene (rectus, right) and S-limonene (sinister, left) where the former smells of oranges and the latter of lemons. Accordingly, the synthesis of enantio-pure products is of the utmost relevance in biochemistry and the pharmaceutical industry. Despite this importance, the potential of chiral metal surfaces for asymmetric catalysis is practically unexplored, not least because the crystal structure of elemental metals is achiral. The intermetallic compound Pd1Ga1 belongs to the space group space group mo. 198, P213 and its bulk structure as well as all its terminating surfaces are chiral. In my presentation, I will introduce the surface structure and properties of the low Miller-index surfaces of Pd1Ga1 investigated by Scanning Tunneling Microscopy (STM) and Low Energy Electron Diffraction (IV-LEED). Then I will review the transfer of the surface chirality to chiral and prochiral molecular systems, where very high enantiomeric excess of up to 99 % can be observed. The chirality of the surface can also manifest itself in directional molecular motion, which we observe in the highly directed rotation of acetylene molecules. The rotation of the molecule can be temperature activated or triggered by the tunneling current of the STM tip, in which case the rotation frequency is highly dependent on the bias voltage. In this activated rotation regime, I will discuss the role of friction as a necessary component to yield the directional rotation. |
13.02.2023
Hybrid Zoom / CN B.425 R.206 |
Pascal Reiss High-pressure studies of electronic structures - past, present and future MPI for Solid State Research, Stuttgart Hydrostatic pressure is one of the most powerful and successful tuning parameters for the experimental
investigation of quantum materials. Ranging from the realisation of unique crystal structures to the observation
of record-high transition temperatures in conventional and unconventional superconductors, hydrostatic
pressure has led to the discovery of many mysterious phases. However, our understanding of such high-pressure
phases is often very limited, in particular regarding their electronic structure. The main reason is the necessity for
a pressure cell, its various components as well as the pressure transmitting media. These render many high-
pressure experimental techniques very challenging or flat out impossible, including many thermodynamic or
photoemission experiments.
In this talk, I will give an overview of various pressure techniques and how we used them recently to reveal the
electronic structure of FeSe-based superconductors. Our work has not only provided groundbreaking insights into
nematic quantum criticality [1], but also revealed the presence of a quantum Griffiths phase [2], as well as a fragile
nature of the high-Tc phase under large pressures [3]. Moreover, I will present our recent developments towards
low-temperature pressure quenches which overcome the technical limitations arising from the presence of the
various pressure components in order to carry out previously impossible thermodynamic measurements on
metastable high-pressure phases [4]. |
07.02.2023
Hybrid Zoom / CS B.30.23, R.3-1 |
Matthias Keßler Magnetic ordering in the Kondo lattice IQMT, KIT Heavy fermion materials are a rich research topic due to their anomalous low-temperature properties. While it is generally accepted that these phenomena are caused by the interplay between itinerant and localized electrons (resulting in the eponymous "heavy" particles), the details of this strongly correlated state are still unclear. Some topics of interest are the quasiparticle dynamics and possible magnetic ordering.In this talk I will present some theoretical calculations for the Kondo lattice model, the simplest model of a heavy fermion material. The problem is attacked using bond fermion theory, a concep- tually simple approach that nonetheless retains much of the strong correlation expected from the system. Special focus is put on antiferromagnetic order, as well as the influence of external magnetic fields and geometric frustration. |
03.02.2023
Hybrid Zoom / CN B.425 R.206 |
Elena Hassinger Interplay of ordered states in CeRh2As2 Institut für Festkörper- und Materialphysik, Technische Universität Dresden Quantum materials are interesting because they host exotic states such as unconventional superconductivity that are valuable for applications. For example, finding a topological odd-parity superconductor would be a breakthrough for quantum computing. The recent discovery of two-phase superconductivity in CeRh2As2, is a big step in this direction, since the observed transition is from even to odd-parity superconductivity. It is rooted in the presence of two Ce sites with locally broken inversion symmetry. The phase-diagram presents clear experimental evidence that local inversion-symmetry breaking is a crucial parameter in the study of quantum materials that can induce odd-parity superconductivity. However, with one material realization, we are far from controlling this parameter. My research currently intends studying exotic quantum states that emerge in materials with locally broken inversion symmetry. By measuring bulk transport and magnetic properties in extreme conditions of very low temperature, high magnetic field and high hydrostatic and uniaxial pressure, we investigate and tune the delicate interplay of local inversion-symmetry breaking with correlated electrons, magnetic, and orbital degrees of freedom and superconductivity. I will give an overview of recent experimental investigations of CeRh2As2 from our group. |
01.02.2023
Zoom |
Rolf W. Lortz Uncovering the secrets of unusual superconductors Department of Physics, The Hong Kong University of Science & Technology In this talk I will provide a relatively broad overview of my work in the field of unusual superconducting states, from thermodynamic characterization of bulk single crystals to quantum spectroscopy in nanoscale devices. I will give several short research examples of how sophisticated home-made calorimetric probes can provide a wealth of information on unusual superconducting states, ranging from phonon spectroscopy and electron-phonon coupling (which is usually only accessible by neutron scattering and tunneling spectroscopy), to the detection of the tiny signature of thermal fluctuations and vortex melting in classical superconductors (where it was previously widely believed to be experimentally inaccessible), to the detection of the superconducting properties in arrays of elementary sub-nanowires, where the specific heat reveals an extreme enhancement of the superconducting critical temperature caused solely by the nanostructuring. I will then discuss three selected topics in more detail: the Fulde-Ferrell-Larkin-Ovchinnikov state (which we have discovered in three different superconductors: the organic superconductor k-(ET)2Cu(NCS)2, the Fe-based superconductor KFe2As3, and most recently in the transition-metal dichalcogenide superconductor NbS2), nematic and topological superconductivity in doped Bi2Se3 and monolayers of NbSe2, and a new platform for the detection of localized Majorana modes in mesoscopic quasi one-dimensional quantum anomalous Hall insulator/superconductor heterostructures. |
31.01.2023
Hybrid Zoom / CN B.425 R.206 |
Diego A. Zocco Materials at the intersection of strong electronic correlations and nontrivial topology Institute of Solid State Physics, Vienna University of Technology (TU Wien) The ability to control topological states at will holds great promise for its application in topological quantum
devices. Heavy fermion compounds are well known for their excellent tunability, and provide an exceptional
platform to explore the intersection of strong electronic correlations and electronic topology. In this talk, I will focus on tuning experiments performed on heavy fermion semimetals in which Weyl nodes form in a setting of
broken inversion and preserved time-reversal symmetries. In Ce3Bi4Pd3, which exemplifies the notion of Weyl-Kondo semimetal (WKSM) [1,2], and in which a giant spontaneous Hall effect has been observed [3], we found
that the application of relatively modest magnetic fields suppresses the topological signatures; we attribute this
effect to the annihilation of Weyl nodes at a topological quantum phase transition [4]. CeRu4Sn6 is another WKSM
candidate material [5]. Interestingly, inelastic neutron scattering experiments revealed that the material is
quantum critical without tuning [6]. I will present pressure-tuning investigations of CeRu4Sn6, and discuss whether
the WKSM state may nucleate out of quantum critical fluctuations [7].
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31.01.2023
Hybrid Zoom / CS B.30.23, R.3-1 |
Mikhail Feigel’man Gapful electrons in a vortex core of granular superconductor Floralis & LPMMC, University Grenoble -Alpes |
24.01.2023
Hybrid Zoom / CS B.30.23, R.3-1 |
Aparajita Singha Non-invasive imaging and coherent control of surface-supported single spins Max-Planck-Institute for Solid State Research, Stuttgart |
17.01.2023
Hybrid Zoom / CS B.30.23, R.3-1 |
Markus Ternes From excitations of individual atomic and molecular spins to topological quasiparticle excitations in a Kondo lattice RWTH Aachen |
