ConQuMat - TRR360

TRR 360 Seminar: !! Canceled due to illness of the speaker !!Designing Quantum Materials with Light Michael Sentef
2025-05-20 16:00 - 17:00 (Europe/Berlin) | University of Augsburg, Room S-288 + Zoom
The seminar talk has been canceled due to illness of the speaker!
Designing Quantum Materials with Light
Prof. Dr. Michael Sentef
Universität Bremen
Max Planck Institute for the Structure and Dynamics of Matter, Hamburg, Germany
In recent years, light-driven quantum materials science has undergone a fundamental transformation. What was once a theoretical vision—the ability to control and manipulate emergent properties of materials on ultrafast timescales—has now become a reality [1]. This progress has been enabled by rapid advancements in shaping laser pulses, probing nonequilibrium dynamics with femtosecond resolution, and developing sophisticated theoretical approaches to describe light-driven many-body systems [2]. As a result, we are now entering an era in which quantum materials can be actively “designed” and controlled using tailored light fields.
A cornerstone of this approach is Floquet engineering, which exploits periodic driving to coherently modify electronic states and induce novel phases of matter. I will briefly review key experimental and theoretical developments in realizing Floquet states in quantum materials and discuss their implications for controlling competing orders. However, despite its promise, Floquet engineering also faces intrinsic limitations, particularly due to heating effects and decoherence, which can constrain its applicability as a general tuning mechanism.
Moving beyond conventional Floquet approaches, a new frontier is emerging: cavity quantum materials [3]. By embedding materials in tailored quantum-electrodynamical environments, such as optical cavities, it is possible to enhance light-matter interactions and create hybrid light-matter states with fundamentally new properties. Unlike classical laser-driven schemes, cavity-mediated interactions can modify quantum fluctuations and collective excitations even in thermal equilibrium, offering a novel route to control material properties without direct external driving. I will highlight recent advances in this field, both from theoretical [4] and experimental [5,6] perspectives, and specifically discuss how strong correlations in cavity quantum materials provide new opportunities for engineering competing electronic orders through light-matter hybridization. This emerging paradigm may open pathways toward controlling superconductivity, charge density waves, and other ordered phases in a fundamentally new way.

Figure: Top left – illustration of a quantum material driven by a classical laser drive. Top right – cavity-embedded quantum material, opening the possibility to use vacuum fluctuations of light to control emergent properties. Bottom – setup of the McIver lab for on-chip THz spectroscopy of quantum materials in a plasmonic cavity [5].
[1] A. de la Torre et al., Rev. Mod. Phys. 93, 041002 (2021)
[2] F. Caruso et al., arXiv:2501.06752
[3] F. Schlawin et al., Applied Physics Reviews 9, 011312 (2022)
[4] M. A. Sentef et al., Phys. Rev. Research 2, 033033 (2020)
[5] G. Kipp, H. Bretscher, et al., arXiv:2403.19745
[6] B. Le Dé et al., Journal of Physics: Materials 5, 024006 (2022); I. Keren, T. Webb, D. Basov, et al., forthcoming

Venue

TRR 360 Seminar: RIXS interferometry: cluster Mott insulators and bond-directional excitations in Kitaev materials Markus Grüninger
2025-05-27 16:00 - 17:00 | University of Augsburg, Room S-288 + Zoom
RIXS interferometry: cluster Mott insulators and bond-directional excitations in Kitaev materials
Prof. Dr. Markus Grüninger
Universität zu Köln

Cluster Mott insulators provide a platform for novel types of quantum magnets with unconventional magnetic moments. Electrons are localized on a cluster such as a dimer and occupy quasimolecular cluster orbitals. In cluster Mott insulators, RIXS interferometry reveals the symmetry and character of excited states, offering a powerful tool to study the electronic structure. We systematically investigate the quasimolecular properties of dimers, trimers, and tetrahedra in the 5d transition-metal compounds Ba3MIr2O9, Ba4NbIr3O12, and GaTa4Se8. Furthermore, we discuss the applicability of the cluster picture for 3d GaV4S8.
RIXS interferometry can also be applied to Kitaev materials such as Na2IrO3 and α-Li2IrO3 and shows distinctive fingerprints of Kitaev physics. Kitaev exchange restricts spin-spin correlations to nearest neighbors, giving rise to a dimer-like dynamical structure factor. Bond-directional exchange implies the existence of bond-directional excitations. Making use of polarization selection rules, RIXS reveals this bond-directional character of magnetic excitations in Na2IrO3.

Venue

TRR 360 Seminar: Randomness, disorder and compromises in magnetic systems Ellen Fogh
2025-06-10 16:00 - 17:00 | University of Augsburg, Room S-288 + Zoom
Randomness, disorder and compromises in magnetic systems
Prof. Dr. Ellen Fogh
Technical University of Munich

The interplay between randomness, disorder and frustration in magnetic systems may bring about interesting ground states and behaviours. Many real materials display intrinsic inhomogeneity, as a result of impurities or (counter)ion substitution, that results in site or bond disorder. This is known as quenched randomness, and the loss of translational symmetry it entails makes the system challenging to study theoretically. However, quenched randomness in magnetic systems can lead to specific ground states with no long-ranged order, including glassy states and the random-singlet state but also various long-range ordered states. Some of these phases of matter are closely related to certain types of quantum spin liquids and thus raise the question of whether randomness in a frustrated system can produce qualitatively different types of quantum coherence, as opposed to only destroying such coherence. Here, I discuss three specific cases of how randomness and disorder have profound consequences for physical behaviour of such magnetic systems.

Venue

TRR 360 Seminar: Some exotic phases for spin-1/2 on the triangular lattice Sylvain Capponi
2025-06-17 14:00 - 15:00 | Technical University Munich + Zoom
Some exotic phases for spin-1/2 on the triangular lattice
Prof. Dr. Sylvain Capponi
Laboratoire de Physique Théorique, Université de Toulouse, CNRS, UPS, France

The triangular lattice is at the origin of magnetic frustration both for Ising or Heisenberg models, as shown by Wannier and Anderson respectively. Hence it is a natural testbed to stabilize unconventional phases of matter. In this talk, I will present two recent numerical studies discussing
(i) the possibility of a Dirac spin liquid in the J1-J2 Heisenberg model [1](ii) the possibility of a supersolid phase in the XXZ model [2] and its relevance to recent scattering experiments on K2Co(SeO3)2

[1] A. Wietek, S. Capponi, and A. Läuchli, Phys. Rev. X 14, 021010 (2024)[2] S. Capponi and A. Läuchli, in preparation

Venue

TRR 360 Seminar: Effect of disorder in a frustrated system Mayukh Majumder
2025-06-24 16:00 - 17:00 | University of Augsburg, Room S-288 + Zoom
Effect of disorder in a frustrated system
Dr. Mayukh Majumder
Department of Physics, Shiv Nadar University, India

Disorder is unavoidable in any real-life quantum many-body system. Though in several cases, the disorder often hinders us from elucidating the actual physics of a system, in some cases, unusual properties can be seen, and exotic phases can be formed due to the presence of disorder. Those interesting phases do not develop in a clean or disorder-free system. Some examples of those exotic phases include the quantum Griffiths phase near quantum criticality, spin glass, random spin singlet state, etc. In the talk, I will discuss the presence of an exotic state, namely the random spin singlet state, stabilized by disorder in a new Copper-based three-dimensional quantum spin liquid candidate.

Venue

TRR 360 Seminar: Signatures of fractional quantum Hall states in few-body systems Cecile Repellin
2025-06-25 14:00 - 15:00 | Technical University Munich + Zoom
Signatures of fractional quantum Hall states in few-body systems
Dr. Cecile Repellin
Université Grenoble Alpes, CNRS, LPMMC, Grenoble, France

Realizing strongly correlated topological phases of ultracold gases is a central goal for quantum gas experiments. Due to the difficulty in preparing these phases, ongoing experiments are focusing on ensembles of few atoms, and the preparation of a fractional quantum Hall state of two bosonic atoms has been achieved [1]. Beyond their preparation, the characterization of these few-body states poses a unique challenge due to their small system size. I will discuss which signatures can be used, and show that hallmark fingerprints of fractional quantum Hall phases, such as a quantized Hall conductivity [2], or chiral edge modes[3], can be extracted in few-particle systems through local density measurements.

[1] Léonard, J., Kim, S., Kwan, J. et al., Realization of a fractional quantum Hall state with ultracold atoms. Nature 619, 495–499 (2023).[2] Repellin, C., Léonard, J. and Goldman, N., Chern insulators of few bosons in a box: Hall plateaus from center-of-mass drifts and density profiles. Phys. Rev. A 102, 063316 (2020).[3] Binanti, F., Goldman, N., Repellin, C, Spectroscopy of edge and bulk collective modes in fractional Chern insulators. Phys. Rev. Research 6, L012054 (2024).

Venue

TRR 360 Sonderseminar: Emergence of novel quantum phases in Yb-based effective spin-1/2 systems with competing exchange interactions Takahiro Onimaru
2025-07-03 11:00 - 12:00 | University of Augsburg, Room S-254 + Zoom
Emergence of novel quantum phases in Yb-based effective spin-1/2 systems with competing exchange interactions

Prof. Dr. Takahiro Onimaru

Hiroshima University, Japan

Venue

TRR 360 Seminar: Frustrated Triangular Lattice Magnetism in Delafossite Type Yb- (and Cr-based) Systems- from spin liquid to field induced order Michael Baenitz
2025-07-08 16:00 - 17:00 | University of Augsburg, Room S-288 + Zoom
Frustrated Triangular Lattice Magnetism in Delafossite Type Yb- (and Cr-based) Systems- from spin liquid to field induced order
Dr. Michael Baenitz
Max-Planck-Institute for Chemical Physics of Solids

Venue

TRR 360 Sonderseminar: Phase diagram of the heavy-fermion superconductor YbRh2Si2 at ultra-low temperatures Manuel Brando
2025-07-08 17:15 - 18:15 | University of Augsburg, Room S-254 + Zoom
Phase diagram of the heavy-fermion superconductor YbRh2Si2 at ultra-low temperatures

Dr. Manuel Brando

Max-Planck-Institute for Chemical Physics of Solids, Dresden

Venue

TRR 360 Seminar: Exploration of Hybrid Skyrmion Systems using Resonant Elastic X-ray Scattering Thorsten Hesjedal
2025-07-22 16:00 - 17:00 | University of Augsburg, Room S-288 + Zoom
Exploration of Hybrid Skyrmion Systems using Resonant Elastic X-ray Scattering
Prof. Dr. Thorsten Hesjedal
Clarendon Laboratory, University of Oxford, UK

A major challenge in topological magnetism lies in the three-dimensional (3D) exploration of the magnetic textures. Recent efforts have focused on understanding how 2D skyrmion sheets vertically stack to form distinct types of 3D topological strings, how these strings behave when clamped at an interface, how they couple across interfaces of dissimilar materials, and how these ordered states can be manipulated. Our team has advanced the capabilities of polarization- and energy-dependent resonant elastic x-ray scattering (REXS) to probe the 3D structure of magnetic skyrmions and related topological objects, as well as their dynamics. In this talk, I will present the latest examples of hybrid skyrmion systems, with a particular focus on 3D objects at or near surfaces and their dynamical properties.

Venue

TRR 360 Seminar: Randomness, disorder and compromises in magnetic systems Ellen Fogh
2025-07-30 14:00 - 15:00 | Technical University Munich + Zoom

TRR 360 Seminar: Imaging Magnetic Dynamics with In-situ and Ultrafast Lorentz Microscopy Sascha Schäfer
2025-11-04 16:00 - 17:00 | University of Augsburg, Room S-288 + Zoom
Imaging Magnetic Dynamics with In-situ and Ultrafast Lorentz Microscopy
Prof. Dr. Sascha Schäfer
Department of Physics, University of Regensburg, Regensburg, GermanyRegensburg Center for Ultrafast Nanoscopy (RUN), Regensburg, Germany
The interaction of magnetic materials with ultrashort light pulses provides intriguing glimpses into the inner workings of the magnetic couplings within a material but also offers an important experimental handle to locally manipulate magnetic textures and phases. Whereas many studies in the field of ultrafast magnetism have utilized various optical pump-probe methodologies, these approaches often lack the required spatial resolution for mapping the nanoscale details of magnetic textures. Here, I will present two methodologies to address ultrafast nanoscale magnetic dynamics in Lorentz microscopy.
In the first part of the talk, I will discuss how in-situ Lorentz microscopy with femtosecond optical excitation [1] can unravel nonlinearities in the magnetic response upon light excitation, focusing on the example of light-induced switching processes in the magnetic texture of Fe3Sn2 thin films [2]. This material hosts dipolar skyrmions [3] which are composed of chiral Bloch-like domain walls in the interior of the film and chiral Néel-like caps at each film surface. Femtosecond light pulses allow for the stochastic switching of the Néel cap chirality. The analysis of switching probabilities yields insights into the importance of interactions within and in-between skyrmions.
In the second part of the talk, I will discuss the current state of ultrafast transmission electron microscopy [4], specifically ultrafast Lorentz microscopy [6], in which femtosecond or picosecond electron pulses enable the stroboscopic imaging of optically or current-driven magnetic dynamics. I will highlight the impact of novel femtosecond electron sources, including radiofrequency beam choppers [7] and laser-driven cold-field emitter sources [8], for different magnetic imaging techniques in electron microscopy, as well as emerging possibilities due to fast electron detectors [9].
[1] T. Eggebrecht; M. Möller et al., Phys. Rev. Lett. 118, 097203 (2017). [2] A Kovács, J. T. Weber et al., Comm. Mat. 6, 223, (2025).[3] L. Kong et al., Phys. Rev. B 107, 174425 (2023).[4] Feist et al., Ultramicroscopy 176, 63 (2017).[5] Feist et al., Nature 521, 200 (2015). [6] N. Rubiano da Silva et al., Phys. Rev. X 8, 031052 (2018).[7] C. Liu et al., Nat. Mat. 24, 406 (2025).[8] A. Schröder et al., Ultramicroscopy 275, 114158 (2025).[9] A. Schröder et al., Ultramicroscopy 256, 113881 (2024).

Venue

TRR 360 Seminar:!! Canceled due to illness of the speaker !! Sebastian Diehl
2025-11-12 14:00 - 15:00 | Technical University Munich + Zoom
Tba
Prof. Dr. Sebastian Diehl
University of Cologne

Venue

TRR 360 Sonderseminar: Computational design of quantum materials using density functional theory and beyond Manish Verma
2025-11-18 16:00 - 17:00 | University of Augsburg, Room S-288
Computational design of quantum materials using density functional theory and beyond

Dr. Manish Verma

Institute for Theoretical Physics and AstrophysicsComputational Quantum MaterialsJulius-Maximilians-Universität Würzburg

Computational design of quantum materials using density functional theory (DFT) and many-body techniques-both perturbative and non-perturbative, has become a powerful tool for exploring key physical phenomena such as strong correlations, metal-to-insulator transitions (MIT), magnetism, and thermoelectricity etc. In this direction, designing novel electronic properties in artificial transition metal oxide (TMO) heterostructures, distinct from their bulk counterparts, has emerged as a new paradigm enabled by modern layer-by-layer growth techniques and the unique nature of d-electrons. I will start my talk by discussing the mechanisms driving the MIT and magnetism in ultrashort-period superlattices (SL), namely (SrVO3)1/(SrTiO3)1(001) [1, 2] and (LaNiO3)1/(LaAlO3)1(001) [3], where confinement and epitaxial strain play fundamental roles. Subsequently, I will present the MIT in Ca-doped LaMnO3, which arises from the interplay between strain and chemical doping [4]. TMO-based SL are also known to exhibit high thermoelectric response, in addition to their environmental friendliness and stability. In this context, I will discuss the doping-induced robust p-type thermoelectric response in ultrashort-period (SrMnO3)1/(SrTiO3)1(001) SL, obtained by employing Boltzmann transport theory within constant-relaxation time approach. Next, I will then present my results on strategies for reducing lattice thermal conductivity in artificial oxide superlattices, obtained using many-body perturbation theory calculations of phonon-phonon interactions. Transition-metal oxides are further known to display strong correlation effects due to their d-electrons. In this regard, LiV2O4 stands out as an enigmatic heavy fermion compound lacking localized f-orbital states. I will present DFT combined with dynamical mean-field theory (DFT+DMFT) results that elucidate the origin of heavy-fermion behavior, supported by angle-resolved photoemission spectroscopy (ARPES) measurements [5].

[1] M. Verma, B. Geisler, and R. Pentcheva, Phys. Rev. B 100, 165126 (2019).[2] M. Verma and R. Pentcheva, Phys. Rev. Research 4, 033013 (2022).[3] M. Verma and R. Pentcheva, Phys. Rev. Research 6 (1), 013189 (2024).[4] S. S. Hong et al., Science 368, 71 (2020).[5] D. Oh et al., Proceedings of the National Academy of Sciences 122 (45), e2518213122 (2025).

Venue

TRR 360 Seminar:A New Perspective on Correlated Metals: from Concealed Mott Quantum Criticality to Disorder in Heavy Fermi Liquids Louk Rademaker
2025-11-19 14:00 - 15:00 | Technical University Munich + Zoom
A New Perspective on Correlated Metals: from Concealed Mott Quantum Criticality to Disorder in Heavy Fermi Liquids

Prof. Dr. Louk Rademaker
Université de Genève, Switzerland

The band-structure picture of metals is very successful in many materials where the electron correlations are weak. On the other extreme, when correlations are very strong, one expects interaction-induced insulators – due to Mott localization or symmetry breaking. However, the intermediate regime where correlations are strong but the material remains gapless, harbors many open questions in our understanding of quantum materials.

In this talk, I will give an overview of three aspects of correlated metals. I will discuss the relation between quantum criticality at the Kondo breakdown and in doped charge-transfer insulators like the cuprates. These metal-to-metal transitions can be viewed as exhibiting concealed Mott criticality.

Near a Mott critical point, large effective mass enhancements are observed. The famous Landau relation between mass enhancement and specific heat requires a new sum rule for the temperature-dependence of the electron self-energy.

In such heavy Fermi liquids, the interplay between correlations and disorder cannot be ignored. Inspired by new experiments on organic compounds, we show that contrary to textbooks, the residual resistivity is affected by the mass enhancement.

Venue

TRR 360 Seminar:Experimental prospects on measurement-altered criticality Sara Murciano
2025-11-26 14:00 - 15:00 | Technical University Munich + Zoom
Experimental prospects on measurement-altered criticality
Prof. Dr. Sara Murciano
Université Paris Saclay, France

Quantum critical systems constitute appealing platforms for the exploration of novel measurement-induced phenomena due to their innate sensitivity to perturbations. I will devise a practical scheme for realizing measurement-altered criticality in a chain of Rydberg atoms tuned to Ising and tricritical Ising phase transitions. Projectively measuring a periodic subset of atoms alters quantum critical correlations in distinct ways that one can control via the choice of measured sites and the measurement outcomes. While this protocol relies on post-selection, the measurement outcomes yielding the most dramatic consequences occur with surprisingly large probabilities.

Venue

TRR 360 Seminar:Multiferroic conversionTsuyoshi Kimura
2025-12-17 16:00 - 17:00 | University of Augsburg, Room 242-R
Multiferroic conversion

Prof. Dr. Tsuyoshi Kimura
Department of Applied Physics, University of Tokyo, Japan

Symmetry breaking ascribed to the evolution of an order parameter is one of the most important concepts in materials physics. Representative examples are symmetry breakings in ferroic materials, such as the symmetry breaking of time reversal in ferro-magnets and that of space inversion in ferroelectrics. Recent research developments of multiferroic materials have triggered extensive studies on unconventional ferroic materials such as ferro-toroidic, ferro-axial, and ferro-chiral materials.

In this presentation, we propose the concept of “multiferroic conversion”, which refers to the transformations of ferroic states by combining different ferroic orders. Such conversion occurs, for example, by a deformation of a structural unit in a ferroic material [1] and by the application of external stimuli such as an electric field to a ferroic material [2-5]. We demonstrate several types of multiferroic conversion by observing unconventional optical phenomena, including electric-field-included Faraday effect (from ferro-magnetic-monopolar to ferro-magnetic state) [2], electrogyration (ferro-axial to ferro-chiral) [3], magneto-chiral dichroism (ferro-axial to ferro-magnetic-toroidal) [4], and electric-field-induced nonreciprocal directional dichroism (altermagnetic to ferro-magnetic-toroidal) [5]. The concept of multiferroic conversion will lead to the unconventional functionalities of various ferroic materials.

[1] T. Nagai et al., J. Am. Chem. Soc. 146, 23348 (2024).[2] T. Hayashida et al., Phys. Rev. Research 4, 043063 (2022).[3] T. Hayashida et al., Nat. Commun. 11, 4582 (2020).[4] T. Hayashida et al., Proc. Natl. Acad. Sci. 120, e2303251120 (2023).[5] T. Hayashida et al., Adv. Mater. 37, 241876 (2025).

Venue
