ConQuMat - TRR360

Spring School 2025
2025-04-07 12:00 - 2025-04-10 17:00 (Europe/Berlin) | das Flax Allgäu, Schlosserstraße 4, Dietmannsried, 87463, Germany
In the middle of the Allgäu TRR360 students, PhDs and Postdocs gather to learn about the topic of Topology for four days. For more information and registration please visit our website.

TRR 360 Seminar: Spin-Orbit Coupling and Emergent Superconductivity in Oxide Heterostructures Dr. Denis Maryenko
2025-03-25 16:00 - 17:00 | University of Augsburg, Room S-288 + Zoom
Spin-Orbit Coupling and Emergent Superconductivity in Oxide Heterostructures
Dr. Denis Maryenko
RIKEN Center for Emergent Matter Science, Wako, Japan
Oxide compounds encompass a diverse class of materials hosting a rich spectrum of quantum phenomena, driven by the interplay of spin-orbit coupling (SOC), electron correlations, and lattice effects. In particular, materials with inherently strong SOC have drawn significant attention due to their potential to stabilize novel electronic phases with implications for future technologies. Controlling these materials and their interfaces provides a powerful route to engineering emergent quantum states.
The perovskite KTaO₃, with its pronounced SOC, has recently emerged as a promising platform for exploring unconventional superconductivity. However, precisely tailoring interfacial electronic states to induce conductivity in KTaO₃ remains a key challenge. In this talk, we present our recent progress on epitaxially grown KTaO₃-based heterostructures, focusing on the LaTiO₃/KTaO₃ interface. Our findings reveal the systematic emergence of superconductivity at this interface, which can be tuned via electric and magnetic fields, pointing to novel superconducting phases. These results provide new insights into the interplay between superconductivity and SOC in low-dimensional systems and establish a robust platform for investigating emergent physics in two-dimensional superconductors.

Venue

Focus Lecture
2025-03-04 10:00 - 11:30 | University of Augsburg Room S-403, Universitätsstrasse 2, Augsburg, 86159
We are pleased to invite you to another focus lecture organized within the framework of the MGK project of TRR360.

Dr. Anton Jesche has kindly agreed to talk about the following topic:

“A Solution for Crystal Growth: Crystal Growth from Solution“

Abstract

Solution growth is a powerful and versatile method for producing high-quality crystals, offering numerous advantages for optimizing sample size, improving crystal quality, and enabling detailed substitution studies. This approach is particularly useful for exploratory research, as it allows crystal growth at lower reaction temperatures, reduced vapor pressures, and with smaller material quantities compared to other techniques. Additionally, solution growth often incorporates an “in situ purification” process, enhancing the quality of the starting materials during crystallization.

The lecture is scheduled for March 4th at 10:00 AM in Room 403S at the Institute of Physics, University of Augsburg.

PhD students are strongly encouraged to attend in person and share this email with interested colleagues. (There will be a bonus for those attending in person.)

For those who cannot join in person, the lecture will also be transmitted via Zoom, the link will be send around via e-mail.

TRR 360 Seminar: Optically induced quantum spin-disordered state in the Kitaev material α-RuCl3 Paul H. M. van Loosdrecht
2025-02-25 14:00 - 15:00 | University of Augsburg, Room S-288 + Zoom
Optically induced quantum spin-disordered state in the Kitaev material α-RuCl3
Prof. Dr. Paul H. M. van Loosdrecht
Universität zu Köln
One way to characterize quantum spin-liquids is through the fractionalization of spin excitations. A prime example of this is found in the exactly solvable Kitaev model of spin-1/2 moments with anisotropic exchange interactions on a tri-coordinated lattice. To find examples of this kind of physics in nature turns out to be challenging. The currently best-known examples of materials in which Kitaev-like physics plays a central role are the layered spin-orbit entangled J=1/2 systems Na2IrO3, α-Li2IrO3, and α-RuCl3. However, these materials all possess additional interactions, which, among other, lead to a magnetically ordered state at low temperature preventing the formation of a pure Kitaev spin-liquid (KSL) state. Apart from the ongoing quest for materials showing a true KSL ground state, one can also destabilize the magnetic order in the existing materials, which potentially can induce the sought-after KSL state. In this contribution I will discuss two methods to destabilize magnetic order in α-RuCl3. The first one is through the application of an in-plane magnetic field. Though it has been shown by various authors that this indeed leads to suppression of the ordered state in α-RuCl3, the nature of the field-induced state is still not fully clear. The second approach is a pump-probe method which creates holon and doublon excitations. These excitations are found to couple efficiently to magnetic excitations which in turn disorder the magnetically ordered state. For sufficiently high excitation densities the magnetic order is fully suppressed, leading to a quantum disordered magnetic state.

Venue

TRR 360 Seminar: Energy relaxation and dynamics in strongly correlated materials N. Peter Armitage
2025-02-13 14:00 - 15:00 | University of Augsburg, Room S-288 + Zoom
Energy relaxation and dynamics in strongly correlated materials
Prof. Dr. N. Peter Armitage
Johns Hopkins University, Baltimore, USA

If a physical system is perturbed from equilibrium, the rate that it equilibrates is an important measure of its physics. In condensed matter systems, we are used to measuring such rates in the context of linear response to electromagnetic fields. For instance, the rate that current decays in a metal after an electric field impulse can be related to the width of its low-frequency “Drude” response in the optical conductivity. The rate that polarization decays after polling a liquid with an E field corresponds to the width of the broad peak in the Debye relaxational functional form. In contrast, the rate of energy relaxation is a fundamental rate that governs many processes in solids, but which is unfortunately not measured straightforwardly via conventional electrodynamic linear response. However quite generically, this rate can be measured in non-linear chi3 spectroscopies. I will discuss recent technical developments in the form of THz range 2D coherent spectroscopy (and its relatives) that allow us to get new information about energy relaxation in correlated and topological metals, as well as disordered electron glasses. I will discuss a number of systems and phenomena in which unconventional dynamics and energy relaxation govern their low energy behavior. I will give number of examples of the power of these new techniques to strongly interacting metals, Dirac semimetals, collective modes in superconductors, electron glasses, and 1D spin chains.

[1] Fahad Mahmood et al., “Observation of a marginal Fermi glass”, Nature Physics (2021).
[2] D. Barbalas et al., “Energy Relaxation and Dynamics in the Correlated Metal Sr2⁢RuO4 via Terahertz Two-Dimensional Coherent Spectroscopy”, Phys. Rev. Lett. 134, 036501 (2025).
[3] K. Katsumi et al., “Revealing novel aspects of light-matter coupling in terahertz two-dimensional coherent spectroscopy: the case of the amplitude mode in superconductors”, Phys. Rev. Lett. 132, 256903 (2024).
[4] R. Bhandia et al., “”Anomalous electronic energy relaxation and soft phonons in the Dirac semimetal Cd3As2“, Phys. Rev. B 110, 075131 (2024).
[5] R. Bhandia et al. “Energy and momentum relaxation through the Curie temperature in an itinerant ferromagnet”, https://arxiv.org/abs/2412.08749.

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TRR 360 Seminar: Cavity electrodynamics of correlated materials in Fabry-Pèrot optical resonators Giacomo Jarc
2025-02-11 16:00 - 17:00 | University of Augsburg, Room S-288 + Zoom
Cavity electrodynamics of correlated materials in Fabry-Pèrot optical resonators
Dr. Giacomo Jarc
Friedrich-Alexander-Universität, Erlangen-Nürnberg

The possibility of engineering collective properties of bulk materials through cavity electrodynamics has been so far mostly explored in theoretical works and theory-based experimental proposals [1]. Only recently, the development of new experimental platforms [2, 3] has started to unlock the full potential of cavity-control of solid-state quantum materials and shed light on new pathways for light-matter coupling in a cavity-confined environment.
In this seminar, I will discuss our recent study on the cavity-mediated thermal control of the metal-to-insulator transition in the charge-density-wave (CDW) material 1T-TaS2 [4], which show the possibility of reversible cavity-manipulation of a phase transition in a correlated material. We embed 1T-TaS2 into cryogenic tunable terahertz cavities [3] and show that a switch between conductive and insulating behaviours, triggered by a large change in the sample temperature, is obtained by mechanically tuning the distance between the cavity mirrors and their alignment. The large thermal modification observed is indicative of a Purcell-like scenario in which the spectral profile of the cavity modifies the energy exchange between the material and the external electromagnetic field [5].
When the cavity is tuned resonantly to the multiple IR-active vibrations of the CDW dielectric phase of 1T-TaS2, we reveal the THz signatures of a multimode vibro-polariton mixing, originating from the collective strong coupling of the CDW vibrations with the cavity field [6]. The estimated components of the polaritonic wave-functions show that the observed multimode polaritons have character from all the vibrational resonances as a consequence of the cavity-mediated hybridization. The Rabi splittings between the hybridized phonons are suppressed across the insulator-to-metal transition as a consequence of the screening of the free charges. Intriguingly, we reveal that in proximity of the phase transition, the phonon dissipations trigger the onset of a weak vibrational coupling regime in the cavity-confined material.
When instead the cavity frequency is tuned within the spectral range of the continuum Drude excitation of 1T-TaS2, we reveal that the quality factor of the cavity, which quantifies the dissipative response of the coupled system, is sensitive to the material phase. We measure indeed the lifetime of the cavity photons to decrease passing from the insulating to the metallic state. This evidence points to a scenario in which the free charges responsible for the Drude excitation can effectively couple to the cavity field and subsequently modulate the light-matter coupling within the Fabry-Pèrot resonator.
Our findings show how cavity electrodynamics can play a role in the intricate equilibrium physics of complex materials, possibly providing a new tool to control and engineer their cooperative properties.

[1] F. Schlawin, D. M. Kennes, and M. A. Sentef., “Cavity quantum materials”, Applied Physics Reviews 9, 011312 (2022).
[2] G. Jarc, S. Y. Mathengattil, F. Giusti, M. Barnaba, A. Singh, A. Montanaro, F. Glerean, E. M. Rigoni, S. Dal Zilio, S. Winnerl, and D. Fausti, “Tunable cryogenic terahertz cavity for strong light-matter coupling in complex materials”, Rev. Sci. Instrum. 93, 033102 (2022).
[3] F. Appugliese, J. Enkner, G. Parravicini-Bagliani, M. Beck, C. Reichl, W. Wegscheider, G. Scalari, C. Ciuti, and J. Faist, “Breakdown of topological protection by cavity vacuum fields in the integer quantum Hall effect”, Science 375, 6584, 1030-1034 (2022).
[4] G. Jarc, S. Y. Mathengattil, A. Montanaro, F. Giusti, E. M. Rigoni, R. Sergo, F. Fassioli, S. Winnerl, S. Dal Zilio, D. Mihailovic, P. Prelovsek, M. Eckstein, and D. Fausti, “Cavity-mediated thermal control of metal-to-insulator transition in 1T-TaS2”, Nature 622, 487-492 (2023).
[5] F. Fassioli, J. Faist, M. Eckstein, and D. Fausti, “Controlling radiative heat through cavity electrodynamics”, arXiv:2403.00851v1 [physics.optics] (2024).
[6] G. Jarc, A. Montanaro, S. Y. Mathengattil, E. M. Rigoni, S. Dal Zilio, and D. Fausti, “Multimode vibrational coupling across the insulator-to-metal transition in 1T-TaS2 in THz cavities”, J. Chem. Phys. 161, 154711 (2024).

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TRR 360 Seminar: Tba Mark Goerbig
2025-01-29 14:00 - 15:00 | Technical University Munich + Zoom
Tba
Prof. Mark Goerbig
Université Paris Sud, Orsay

Venue

TRR 360 Seminar: Directional amplification, non-Hermitian topology, and optomechanical realisation of the bosonic Kitaev chain Andreas Nunnenkamp
2024-12-18 14:00 - 15:00 | Technical University Munich + Zoom
Directional amplification, non-Hermitian topology, and optomechanical realisation of the bosonic Kitaev chain
Prof. Andreas Nunnenkamp
Universität Wien

Directional amplification, in which signals are selectively amplified depending on their propagation direction, has attracted much attention as a key resource for applications, including quantum information processing. I will present a unifying framework based on non-Hermitian topology to understand non-reciprocity and directional amplification in driven-dissipative cavity arrays. Specifically, I will unveil a one-to-one correspondence between a non-zero topological invariant defined on the spectrum of the dynamic matrix and regimes of directional amplification, in which the end-to-end gain grows exponentially with the number of cavities. I will show how to restore the bulk-boundary correspondence for one paradigmatic class of non-Hermitian Hamiltonians. Finally, I will present experiments on a bosonic analog of the fermionic Kitaev chain in an nano-optomechanical network. Our work opens up new avenues in topological photonics and non-Hermitian phases of matter.

C.C. Wanjura, M. Brunelli, and A. Nunnenkamp,
Topological framework for directional amplification in driven-dissipative cavity arrays,
Nat Commun 11, 3149 (2020).
https://doi.org/10.1038/s41467-020-16863-9

M. Brunelli, C.C. Wanjura, and A. Nunnenkamp,
Restoration of the non-Hermitian bulk-boundary correspondence via topological amplification,
SciPost Phys. 15, 173 (2023).
https://scipost.org/10.21468/SciPostPhys.15.4.173

J.J. Slim, C.C. Wanjura, M. Brunelli et al.,
Optomechanical realization of the bosonic Kitaev chain,
Nature 627, 767 (2024).
https://doi.org/10.1038/s41586-024-07174-w

Venue

TRR 360 Seminar: Tba Urban Seifert
2024-12-04 14:00 - 15:00 | Technical University Munich + Zoom
Tba
Dr. Urban Seifert
TU Dresden

Venue

Young Researcher Forum 2024 + Focus Lecture
2024-11-20 09:30 - 19:00 | TUM Institute of Advanced Study, Lichtenbergstraße 2a, Garching, 85748
Dear young researchers,

let’s meet again for another YR Forum! This year we will meat in Garching near Munich and learn how to master the art of salary negotiations with Claudia Kimich. Of course also a labtour of our colleagues of the TUM will be given and we will hear Alexander Tsirlin and Johannes Knolle talk about “Quantum Spin Liquids”. To register and get more information visit our webpage!

TRR 360 Seminar: Multi-Extreme THz ESR Study of the Pressure-Induced Phase Transition in the Shastry-Sutherland Model Substance SrCu2(BO3)2 Hitoshi Ohta
2024-11-12 16:00 - 17:00 | University of Augsburg, Room S-288 + Zoom
Multi-Extreme THz ESR Study of the Pressure-Induced Phase Transition in the Shastry-Sutherland Model Substance SrCu2(BO3)2
Prof. Dr. Hitoshi Ohta
Molecular Photoscience Research Center, Kobe University, JapanResearch Center for Development of Far-Infrared Region, University of Fukui, Japan
We have been developing THz ESR under multi-extreme conditions, such as high magnetic field, high pressure and low temperature in Kobe. It covers the frequency region between 0.03 and 7 THz,1 the temperature region between 1.8 and 300 K,1 the magnetic field region up to 55 T,1 and the pressure region is extended from 1.5 GPa2 to 2.5 GPa using the hybrid-type piston-cylinder pressure cell.3 It also includes mechanically detected ESR4 measurements using a commercially available membrane-type surface stress sensor, which is the extension from our micro-cantilever ESR5. As an example, application of high pressure THz ESR to understand the pressure-induced phase transition in the Shastry-Sutherland model substance SrCu2(BO3)2 will be discussed. Using our technique, we were able to determine the pressure where the pressure-induced phase transition occurs, and obtain the pressure dependence of exchange interactions in SrCu2(BO3)2 [Ref. 6]. Comparison of our results with the theory will be discussed.

H. Ohta et al., J. Low Temp. Phys. 2013, 170, 511.
T. Sakurai et al., Rev. Sci. Inst. 2007, 78, 065107
K. Fujimoto et al., Appl. Mag. Res. 2013, 44, 893; H. Ohta et al., J. Phys. Chem. B 2015, 119, 13755; T. Sakurai et al., J. Mag. Res., 2015, 259,108.
H. Takahashi et al., Rev. Sci. Intrum. 2018, 89, 036108
H. Ohta et al., AIP Conf. Proceedings 2006, 850, 1643; E. Ohmichi et al., Rev. Sci. Instrum. 2008, 79, 103903; H. Takahashi et al., Appl. Phys. Lett. 2015, 107, 182405.
T. Sakurai et al., J. Phys. Soc. Jpn. 87 (2018) 033701

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TRR 360 Seminar: Imaging superconductors at high pressure using a nanoscale quantum sensor Christopher Laumann
2024-11-06 14:00 - 15:00 | Technical University Munich + Zoom
Imaging superconductors at high pressure using a nanoscale quantum sensor
Christopher LaumannBoston University, USA

Pressure alters the physical, chemical and electronic properties of matter. By compressing a material between two opposing brilliant cut diamonds, the diamond anvil cell enables tabletop experiments to reach pressures more than a million times that of atmospheric pressure. Since its development over half a century ago, it has enabled experiments to directly access pressure as a thermodynamic tuning parameter and has had a dramatic impact on quantum science, chemistry and materials physics. Among these impacts, a tremendous amount of recent attention has focused on the discovery of superconductivity in a class of hydrogen-based materials. When compressed to megabar pressures, these so-called super-hydrides are believed to exhibit the highest known critical temperatures, and have led to a nascent field that is equal parts exciting and controversial. Part of this controversy stems from the nature of the tool itself: especially at high pressures, it is tremendously challenging to extract local information from within a diamond anvil cell.

We describe a new approach to directly “see” the physics inside the sample chamber of a diamond anvil cell at ultra-high pressures. The basic idea is deceptively simple: we directly integrate a thin layer of quantum sensors, the NV defect, into the surface of the diamond anvil that is actually applying the pressure. We demonstrate the ability to perform optical diffraction-limited imaging of both stress fields and magnetism, with the latter allowing us to image the magnetic field expulsion associated with superconductivity. Applying our techniques to cerium hydride, we observe the dual signatures of superconductivity: diamagnetism characteristic of the Meissner effect and a sharp drop of the resistance to near zero. By locally mapping both the diamagnetic response and flux trapping, we directly image the geometry of superconducting regions, showing marked inhomogeneities at the micron scale.

Primary ref:[1] P. Bhattacharyya et al., Nature 627, 73–79 (2024).

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Introduction to the electronic lab book ELabFTW
2024-10-30 09:00 - 10:30
An introduction to the electronic lab book eLabFTW is scheduled for next Wednesday, October 31st at 9:00 a.m. in the seminar room of EPII (room 344, north) at the University of Augsburg.This will be a hybrid seminar, conducted in parallel online.The Zoom link and login details are provided by email to all TRR 360 staff members.

TRR 360 Seminar: Hidden multipolar order and singlet magnetism in f-electrons systems Sergii Khmelevskyi
2024-10-22 16:00 - 17:00 | University of Augsburg, Room S-288 + Zoom
Hidden multipolar order and singlet magnetism in f-electrons systems
Dr. Sergii Khmelevskyi
TU Wien
The nature of order in low-temperature phases of some materials is not directly seen by experiment. Such “hidden orders” (HOs) may inspire decades of research to identify the mechanism underlying those exotic states of matter. In insulators, HO phases originate in degenerate many-electron states on localized f-shells that may harbor high-rank multipole moments. We show how the ground-state order and magnetic excitations of a prototypical HO system NpO2, can be fully described by a low-energy Hamiltonian derived by a many-body ab initio force theorem method. A primary non collinear order of time odd rank 5 (triakontadipolar) moments has been predicted. We show also that exotic non-chiral magnetic order in PrO2 is a results of a strong high order multipolar interactions within whole |JM> ground state multiplet. The multipolar interactions also leads to the peculiar magnetization process in PrO2 resulting in the exotic meta-magnetic transition in the applied magnetic field and fully dominate the ordinary dipolar Heisenberg exchange.
As has been shown by Kotliar and Haule in 2007 the canonical and perhaps most investigated metallic “hidden” order materials URu2Si2 can also develop a “hidden” multipolar order (hexadecapolar) due to localized 5f2 configuration at low temperature. Whereas at higher temperatures a hybridization of the localized 5f-levels leads to the Kondo behavior (“Kondo arrest scenario”) and at very low temperature a hidden order phase coexists with superconductivity. We reveal on basis of correlated ab-intio calculations a close analogy between normal state behavior of URu2Si2 and newly discovered heavy fermion UTe2 superconductor.

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Focus Lecture
2024-10-18 10:30 - 12:00 | University of Augsburg Room S-403, Universitätsstrasse 2, Augsburg, 86159
We are pleased to invite you to the first focus lecture organized within the framework of the MGK project of TRR360.

Dr. Joachim Deisenhofer has kindly agreed to “break the ice” with the following topic:

“THz Time-Domain Spectroscopy in Magnetic Insulators”

In this lecture, Dr. Deisenhofer will introduce the basic concepts of THz time-domain spectroscopy, covering both

theoretical and experimental aspects. The talk will be structured into two key parts:

Basic Principles: A discussion on the foundational concepts of THz time-domain spectroscopy, including how to extract optical material parameters, such as the complex refractive index, from raw data.

Experimental Insights: The second part will highlight experimental results from insulating magnets, particularly in materials such as the magnetoelectric compound Fe₂Mo₃O₈ and the ferrimagnetic spinelFeCr₂S₄.

The lecture is scheduled for October 18th at 10:30 AM in Room 403S at the Institute of Physics, University of Augsburg.

PhD students are strongly encouraged to attend in person and share this email with interested colleagues. (There will be a bonus for those attending in person.)

For those who cannot join in person, the lecture will also be transmitted via Zoom. The Zoom link was send around via e-mail.

Retreat Meeting 2024
2024-10-10 12:00 - 2024-10-11 16:00 | Schloss Hirschberg, Hirschberg 70, Beilngries, 92339, Germany
From 10th to 11th of October all members of the TRR360 meet at castle Hirschberg in Beilngries to share latest results and discuss organizational topics of the TRR.

The program can be downloaded here:

Programm_Retreat Meeting 2024Download

Workshop: Strong and confident in the application process
2024-10-09 12:00 - 20:00 | Schloss Hirschberg, Hirschberg 70, Beilngries, 92339, Germany
Only for our young female researchers!
In this workshop we will look at our strengths, learn about how to built up more self-confidence and how we successfully present ourself during a job application.

MGK Workshop
2024-08-28 08:00 - 2024-08-30 17:00 | Haus der bayerischen Landwirtschaft, Rieder Str. 70, Herrsching am Ammersee, 82211, Germany
The first MGK Workshop will take place in Herrsching am Ammersee!
Many scientific presentations from young researchers, a Gender equality and Diversity workshop, swimming in the Ammersee and many nice hours together are awaiting you. Here, you can check out the detailed MGK Workshop program.
See you in Herrsching!

TRR 360 Seminar: Strain Tuning of Frustrated Magnets and Mott Insulators: Stress Reduces Frustration Andrej Pustogov
2024-07-23 16:00 - 17:00 | University of Augsburg, Room S-288 + Zoom
Strain Tuning of Frustrated Magnets and Mott Insulators: Stress Reduces Frustration
Andrej Pustogov TU Wien
Tuning materials properties on demand is at the heart of condensed matter science. Charge transport and magnetism are strongly linked to the overlap of electronic wave functions and can be, thus, manipulated by varying the electronic bandwidth through chemical substitution or physical pressure. Yet, a controlled variation of the symmetry, anisotropy and frustration of transfer integrals and exchange interactions remained inaccessible so far.
Here, we explore Mott insulators subject to strong antiferromagnetic interactions, where geometrical frustration suppresses magnetic order entirely [1,2] or down to very low temperatures TN << J [4,7]. Utilizing the recent advancements in strain tuning of unconventional superconductors [8,9], we apply uniaxial stress to fine-tune the Mott transition with unprecedented precision in a triangular-lattice compound [2]. Through the slope of the metal-insulator boundary in the temperature-pressure phase diagram we pinpoint the nonmagnetic ground state of the most intensely studied quantum-spin-liquid candidate [1-3]. By applying in situ uniaxial pressure to a clean, well-studied kagome-lattice compound without disorder [4-6], we obtain direct control of antiferromagnetic order within one single crystal [7]. As the applied stress reduces the frustration strength, TN is enhanced by 10% [7]. Our pioneering endeavors [2,7] demonstrate uniaxial strain as a powerful tool to tune interacting spins on frustrated lattices – towards stabilizing novel, exotic, possibly even quantum entangled spin states.
[1] B. Miksch, A. Pustogow, M. Javaheri Rahim, A. A. Bardin, K. Kanoda, J. A. Schlueter, R. Hübner, M. Scheffler, M. Dressel, Science 372, 276-279 (2021)[2] A. Pustogow, Y. Kawasugi, H. Sakurakoji, N. Tajima, Nat. Commun. 14, 1960 (2023)[3] Y. Kawasugi, S. Yamazaki, A. Pustogow, N. Tajima, J. Phys. Soc. Jpn. 92, 065001 (2023)[4] P. Puphal, M. Bolte, D. Sheptyakov, A. Pustogow, K. Kliemt, M. Dressel, M. Baenitz, C. Krellner, J., Mater. Chem. C 5, 2629 (2017)[5] T. Biesner et al., Adv. Quantum Technol. 2022, 2200023 (2022)[6] D. Chatterjee et al., Phys. Rev. B 107, 125156 (2023)[7] Jierong Wang, Y.-S. Su, M. Spitaler, K.M. Zoch, C. Krellner, P. Puphal, S.E. Brown, and A. Pustogow, Phys. Rev. Lett. 131, 256501 (2023)[8] C.W. Hicks et al., Science 344, 283 LP (2014)[9] A. Chronister et al., npj Quantum Mater. 7, 113 (2022)

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TRR 360 Seminar: Discerning and mitigating complex quantum correlations in many-body dynamics Jan Budich
2024-07-17 14:00 - 15:00 | Technical University Munich + Zoom
Discerning and mitigating complex quantum correlations in many-body dynamics
Jan BudichTU Dresden
The proliferation of complex quantum correlations in many-body dynamics poses a formidable challenge both to quantum information science at a fundamental level and to classical variational approaches such as tensor network methods at a practical computational level. In this talk, after a brief introduction to the broader field, we discuss two of our recent contributions towards discerning various sources of quantum correlations and mitigating dynamical growth of entanglement. First, noting that entanglement depends on how a system is partitioned into subsystems (entanglement cut), we explore the potential of dynamically adjusting the entanglement cut as a strategy for reducing entanglement growth. Second, regarding the dynamics of mixed states such as locally perturbed thermal states, we demonstrate how tools from differential geometry such as parallel transport can be harnessed to tame the temporal growth of quantum correlations in a purified state corresponding to the physical mixed state.

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MGK industry visit
2024-07-15 13:00 - 17:00 | Attocube Systems AG, Eglfinger Weg 2, Haar, 85540, Germany
Interested MGK young researchers can visit two leading companies in quantum technologies in Munich.
The first one is Attocube Systems AG (Eglfinger Weg 2, 85540 Haar, https://www.attocube.com/en), which is known for its precision nanopositioning systems. We will meet there at 1 pm.
At 4 pm the second tour starts at the Kiutra GmbH (Flößergasse 2, 81369 Munich, https://kiutra.com/). This company is renowned for its advancements in cryogen-free refrigeration .

TRR 360 Sonderseminar: Optimization and Application for Cryogenic Magnetic Refrigeration Using Yb-based Intermetallic Compounds Yasuyuki Shimura
2024-06-28 10:00 - 11:00 | University of Augsburg, Room 242-R
Optimization and Application for Cryogenic Magnetic Refrigeration Using Yb-based Intermetallic Compounds
Prof. Dr. Yasuyuki Shimura
Hiroshima University, Japan

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TRR 360 Sonderseminar: Ultrafast spin-orbitronics with terahertz electromagnetic pulses Tobias Kampfrath
2024-06-27 14:00 - 15:00 | University of Augsburg, Room S-288 + Zoom
Ultrafast spin-orbitronics with terahertz electromagnetic pulses
Tobias Kampfrath
Freie Universität Berlin and Fritz Haber Institute of the Max Planck Society, Berlin

To take advantage of the electron spin in future electronics, spin angular momentum needs to be transported and detected. Electric fields and temperature gradients have been shown to efficiently drive spin transport at megahertz and gigahertz frequencies. However, to probe the initial elementary steps that lead to the formation of spin currents, we need to launch and measure transport on much faster, i.e., femtosecond time scales.
To achieve this goal, we apply optical femtosecond laser pulses to induce a spin voltage in a metallic ferromagnetic layer F [1]. The resulting spin current into an adjacent layer is measured by conversion into a charge current in a layer N and detection of the concomitantly emitted terahertz electromagnetic pulse [2]. Interesting applications such as terahertz spin-conductance spectroscopy [3] and the generation of ultrashort terahertz electromagnetic pulses emerge [4]. In all cases, the emitted terahertz signal arises from regions close to the F/N interface, thereby making spintronic terahertz emission very interface-sensitive [5]
This methodology can be transferred from the spin to the so far highly unexplored orbital angular momentum of electrons. We obtain new insights into orbitronic phenomena on their natural time scales, for example, time-domain signatures of giant propagation lengths of orbital currents in tungsten [6].
Finally, one can implement a reciprocal experimental scheme and use intense terahertz electromagnetic pulses to drive electric currents and control magnetic order on ultrafast time scales through, for example, Néel spin-orbit torques [7].

References[1] Rouzegar et al., Phys. Rev. B 106, 144427 (2022)[2] Kampfrath et al., Nature Nanotech. 8, 256 (2013)[3] Rouzegar et al., arXiv:2305.09074 (2023)[4] Seifert et al., Nature Photon. 10, 483 (2016); Rouzegar et al., Phys. Rev. Appl. 19, 034018 (2023)[5] Gueckstock et al., Advanced Materials 33, 2006281 (2021)[6] Seifert et al., Nature Nanotech. 18, 1132-1138 (2023)[7] Behovits et al., Nature Communications 14, 6038 (2023)

Figure: Schematic of optically driven spin-orbitronic emission of ultrabroadband terahertz electromagnetic pulses from a generic F|N thin-film stack. 𝑴 is the magnetization of layer F.

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TRR 360 Seminar: Fractionalized magnetization plateaus with hidden discrete degeneracy in metallic Kagome spin ice HoAgGe Kan Zhao
2024-06-25 16:00 - 17:00 | University of Augsburg, Room S-288 + Zoom

TRR 360 Seminar: Twisted Bilayer Graphene: a platform for heavy fermion physics Roser Valenti
2024-06-12 14:00 - 15:00 | Technical University Munich + Zoom
Twisted Bilayer Graphene: a platform for heavy fermion physics
Roser ValentiGoethe-Universität Frankfurt am Main
After a brief introduction to TBG, we will discuss its correlated and topological properties and put forward a heavy fermion description. We will show through a combination of Hartree-Fock (HF) and Dynamical Mean Field Theory (DMFT) that such a heavy fermion picture is able to describe in a unified way many of the experimentally observed features in these materials.

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TRR 360 Sonderseminar: Structure and magnetism of LMO/SMO superlattices Vasily Moshnyaga
2024-06-11 16:00 - 17:00 | University of Augsburg, Room S-288 + Zoom
Structure and magnetism of LMO/SMO superlattices
Prof. Dr. Vasily MoshnyagaI. Physikalisches InstitutGeorg-August-Universität Göttingen
Heterostructures of strongly correlated oxides, like superlattices (SLs) of (LaMnO3)m/(SrMnO3)n ((LMO)m/(SMO)n), provide a rich platform for searching emergent phases at the interfaces as well as to design artificial electronically/chemically inhomogeneous materials to study the manifestations of electron-spin-lattice correlations in reduced dimensions. We studied the structure and magnetism of the LMO/SMO SLs prepared on SrTiO3(100) substrates by metalorganic aerosol deposition (MAD) technique. The role of interfacial charge transfer in the high-TC emergent ferromagnetism and the interrelations between the octahedral tilt/rotation angle, controlled by LMO/SMO ratio, and magnetic/thermal properties have been elucidated. Further on, we have grown LMO/SMO SLs with gradual La/Sr compositional modulations on the scale 5-10 u.c. and studied their role in the development of high- and low-temperature magnetic phases. We propose a route to grow strongly correlated heterostructures with modulated electronic properties at the nanoscale.

Venue

TRR 360 Sonderseminar: Microwave spectrum analyzer based on a rapidly tuned spin-torque nano-oscillator Andrei Slavin
2024-06-11 14:00 - 15:00 | Technical University Munich + Zoom
Microwave spectrum analyzer based on a rapidly tuned spin-torque nano-oscillator
Andrei Slavin
Department of Physics, Oakland University, Rochester, MI 48309, USA
A spintronic method of ultra-fast broadband microwave spectrum analysis is proposed. It uses a rapidly tuned spin torque nano-oscillator (STNO) and does not require injection locking. This method treats an STNO generating a microwave signal as an element with an oscillating resistance. When an external signal is applied to this “resistor” for analysis, it is mixed with the signal generated by the STNO. The resulting mixed voltage contains the “sum” and “difference” frequencies, and the latter produces a DC component when the external frequency matches the frequency generated by the STNO. The mixed voltage is processed using a low pass filter to exclude the “sum” frequency components and a matched filter to exclude the dependence of the resultant DC voltage on the phase difference between the two signals. It is found analytically and by numerical simulation that the proposed spectrum analyzer has a frequency resolution at a theoretical limit in a real-time scanning bandwidth of 10 GHz and a frequency scanning rate about 20 MHz /ns, while remaining sensitive to signal power as low as the Johnson-Nyquist thermal noise floor.

Andrei Slavin received PhD degree in Physics in 1977 from the St.Petersburg Technical University, St. Petersburg, Russia. Dr. Slavin developed a state-of-the-art theory of spin-torque oscillators, which has numerous applications in the theory of current-driven magnetization dynamics in magnetic nanostructures. His current research support includes multiple grants from the U.S. Army, DARPA, SRC and the National Science Foundation. This research involves international collaborations with leading scientists in many countries, including Germany, Ukraine, France, Italy, and the United States. Dr. Slavin is a frequently invited speaker at magnetism conferences around the world.
Andrei Slavin is Fellow of the American Physical Society, Fellow of the IEEE, and Distinguished Professor and Chair of the Physics Department at the Oakland University, Rochester, Michigan, USA.

Venue

TRR 360 Seminar:Exploring quantum impurities and measurement backaction via tensor-networksOded Zilberberg
2024-05-22 14:00 - 15:00 | Technical University Munich + Zoom
Exploring quantum impurities and measurement backaction via tensor-networks
Oded Zilberberg
Universität Konstanz

Tensor networks allow us to compress and efficiently represent one-dimensional many-body states. This relies on truncating small correlations and entanglement along the system’s length. At the same time, the representation provides easy access to these correlations. My talk will be divided into three parts: (i) I will introduce a mesoscopic coupled quantum-dots system, map it onto a Wilson chain, and show how to study Kondo physics via the tensor network correlations as order parameters, (ii) I will introduce how the tensor network description of a mixed state provides an easy-to-read entanglement measure for open systems, and (iii) show how the entanglement measure allows us to better understand measurement-induced transitions (MITs).

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Steering Committee Meeting
2024-05-14 12:00 - 13:00

TRR 360 Seminar: Altermagnetism: spin symmetry prediction and photoemission observation Libor Šmejkal
2024-05-07 16:00 - 17:00 | University of Augsburg, Room S-288 + Zoom
Altermagnetism: spin symmetry prediction and photoemission observation

Libor ŠmejkalUniversity of Mainz

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