TRR 360 Seminar: Imaging Magnetic Dynamics with In-situ and Ultrafast Lorentz Microscopy Sascha Schäfer
2025-11-04 16:00 - 17:00 (Europe/Berlin) | 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).

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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

TRR 360 Seminar:From solitons to correlations: Non-equilibrium spin dynamics across multiple scales Lukas Körber
2026-04-28 16:00 - 17:00 | University of Augsburg, Room S-288 + Zoom
From solitons to correlations: Non-equilibrium spin dynamics across multiple scales

Dr. Lukas Körber
Ultrafast Spectroscopy of Correlated Materials, Radboud University, Nijmegen, Netherlands

Although magnetism fundamentally arises from complex quantum many-body interactions, it is often possible to describe phenomena in ordered materials using classical emergent frameworks at various length and energy scales. This perspective facilitates the analysis of a wide range of static and dynamic nonlinear phenomena, including topological solitons, spin textures, parametric resonance, ultrafast switching, auto-oscillations, and chaos. Typically, each emergent level is achieved by coarse-graining microscopic details, which provides predictive power and introduces new conceptual tools, such as torques, conserved topological charges, and solitons. However, when magnetic systems are driven far from equilibrium, this established hierarchy of emergent descriptions can break down, resulting in fundamentally new multiscale effects that challenge existing conceptual frameworks.

In this talk, I will present three complementary mechanisms that exemplify this breakdown from distinct perspectives. First, driving a topological soliton with high-frequency microwave radiation can push the magnetic system into a far-from-equilibrium state where slow soliton dynamics and fast magnon dynamics become strongly coupled, resulting in self-induced Floquet modes [1]. Second, strong laser excitation of chiral magnets can induce significant thermal fluctuations, resulting in the ultrafast nucleation of solitons known as skyrmions. While the skyrmion number is typically considered conserved at the emergent level, in the ultrafast regime, their collective dynamics can be described by independent thermally activated nucleation and annihilation events [2]. Lastly, at even shorter spatiotemporal scales, perturbing antiferromagnets can drive them into strongly excited states where classical nonlinear magnetism fails, and quantum correlations become significant. Although numerical quantum many-body techniques can capture certain nonlinear spin dynamics, these methods are computationally intensive and often obscure the connection between nonlinear dynamics and their geometric origin in the angular-momentum algebra of spins. To address this challenge, we propose a semiclassical spin-correlation theory that evolves spin correlations on lattice bonds rather than on individual spins [3]. This approach incorporates nonlinear dynamics beyond classical models while preserving the geometric structure associated with the intrinsic nonlinearity of spins.[1] Heins, Körber et al., Science 391, 6781pp. 190-194 (2026), DOI: 10.1126/science.adq9891[2] Lieferink, Körber et al., PRL 136, 146705 (2026), DOI: 10.1103/brnt-2m9l[3] Körber et al. (2025), arXiv:2512.11466

Venue

TRR 360 Seminar:tbdMathias Kläui
2026-07-14 16:00 - 17:00 | University of Augsburg, Room S-288 + Zoom
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Prof. Dr. Mathias Kläui
Institute of Physics, University of Mainz

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