TRR360 International Conference on
Constrained Quantum Matter

22-25 September 2025

Monastery Ettal

Ettal Monastery

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Topics

Magnetic Band Topology – Entangled States of Matter – Non-equilibrium Dynamics

List of invited speakers

  • Allen Scheie (Los Alamos National Lab, USA)
  • Alexey Kimel (Radboud University, Netherlands)
  • Anna Keselman (Technion, Israel)
  • Axel Hoffmann (University of Illinois, USA)
  • Binghai Yan (Penn State, USA)
  • Daniele Fausti (FAU, Germany)
  • Flore Kunst (MPL, Germany)
  • Jeroen van den Brink (IFW Dresden, Germany)
  • Joachim Wosnitza (HZDR, Germany)
  • Lei Shu (Fudan University, China)
  • Manila Songvilay (Institut Neel, France)
  • Milan Orlita (LNCMI, France)
  • M. Zahid Hasan (Princeton University, USA)
  • Oksana Zaharko (PSI, Schwitzerland)
  • Peter Armitage (JHU, USA)
  • Riccardo Comin (MIT, USA)
  • Rosario Fazio (ICTP, Italy)
  • Roser Valenti (University Frankfurt, Germany)
  • Veronika Sunko (ISTA, Austria)
  • Yuan Li (Institute of Physics, CAS, China)
  • Yoshinori Tokura (Riken, Japan)

Program

DETAILED PROGRAM International Conference
PROGRAM International Conference + Retreat
DETAILED PROGRAM Int. Conf. + Retreat

I present a study of the quantum spin dynamics of 2D triangular magnet KYbSe2, studied via real-space correlations and entanglement measures. Previous studies have shown that magnetic neutron scattering can be Fourier transformed from frequency and reciprocal space into time and real space. We perform such analysis for KYbSe2, which is proximate to a quantum spin liquid phase and behaves as one at finite energy-scales. We compare this real-space dynamics to a variety of theoretical calculations, which reveals certain behaviors that are not obvious in reciprocal space. Unlike in the 1D Heisenberg chain, the spinon signatures are not obviously visible in the data. However, we observe a nonlinear light cone in KYbSe2 that theoretical calculations struggle to capture. This suggests a low-temperature sub-ballistic transport in the 2D triangular lattice that is presumably driven by its highly entangled and nontrivial quantum dynamics.

Antiferromagnets represent the largest, least explored, arguably the most counterintuitive and thus the most appealing class of magnets in nature. In my talk I will progressively transition from equilibrium to ultrafast out-of-equilibrium physics of antiferromagnets, highlighting three fundamental pillars that make these materials qualitatively distinct, and often anti-intuitive, compared to their ferromagnetic
counterparts:


1) The antiferromagnetic Néel vector, which is used to describe the order in antiferromagnets, does not strictly qualify as either a purely axial or purely polar vector.
2) Even though the net magnetization is strictly zero in thermodynamic equilibrium of an antiferromagnet, this equality does not necessarily hold during antiferromagnetic spin dynamics.
3) Unlike magnetization, which is associated with net angular momentum, the antiferromagnetic Néel vector is not associated with any fundamentally conserved quantity.


As a result, while commonly accepted Curie-Neumann’s principle states that “the symmetries of the causes are to be found in the effects” [1] and implies that a magnetic field cannot control antiferromagnetic Néel vector, rapidly changing THz magnetic field appears to “violate” this principle and can effectively excite spins in antiferromagnets . In this ultrafast regime, laser-induced spin dynamics
in antiferromagnets is intrinsically non-linear [2-4], where new channels of spin-lattice interaction open-up [2,3], the principle of superposition fails, i.e. 1+1¿2 [4], and antiferromagnets appear to host even more channels to excite spins [5-7] than one can find in ferromagnets. As such, antiefrromagnets stand out not only as counter-intuitive topic for fundamental research but also as a promising platform
for next-generation ultrafast and low-dissipation spintronic technologies.


[1] P. Curie, J. Phys. Theor. Appl., 393–415 (1894) [2] E. A. Mashkovich et al., Science 374, 1608-1611 (2021) [3] T. Metzger et al., Nature Communications 15, 5472 (2024). [4] T. G. H. Blank et al., Phys. Rev. Lett. 131, 096701 (2023).
[5] Y. Behovits et al., Nature Communications 14, 6038 (2023). [6] V. Bilyk et al., Newton 1, 6100132, (2025). [7] R. M. Dubrovin, A. V. Kimel, A. K. Zvezdin, Phys. Rev. B 112, 064402 (2025).

The model of spin-1/2s on the triangular lattice with nearest- and next-nearest-neighbor  antiferromagnetic Heisenberg interactions is central in the search for quantum spin liquids (QSL). While the exact nature of the spin liquid it hosts remains debated and the experimental search for materials within the spin liquid regime is ongoing, we study the magnetization process of the model, aiming for novel insights for both theory and experiment.


Employing large scale density matrix renormalization group (DMRG) studies on finite-circumference cylinders we obtain the ground state phase diagram of the J1 − J2 model in a field. We find good overall agreement with previous semiclassical studies, with several key differences of important implications for future experimental studies. In particular, in the regime of large J2 we observe the formation of a novel 1/2-magnetization plateau. Importantly, we observe that the two magnetization plateaus at 1/3 and 1/2 of the saturation value penetrate beyond the first-order phase transition line at J2/J1 = 1/8 expected semiclassically resulting in a range of J2 values, overlapping with the range in which a QSL is expected at zero field. This observation could serve as a tell-tale in future experimental studies that a material under investigation is in the spin liquid regime.

Magnons readily interact with a wide variety of different excitations, including microwave and optical photons, phonons, and other magnons. Such hybrid magnon dynamic excitations have recently gained increased interest due to their potential impact on coherent information processing [1]. This in turn opens new pathways for hybrid quantum information systems [2–4]. I will discuss specific examples and strategies, where we developed fully integrated devices that form the essential building blocks for more complex integrated coherent quantum systems. Towards this end, we demonstrated strong magnon-photon coupling in scalable coplanar devices using coplanar  superconducting microwave photon resonators [5]. Based on this concept we have shown how two magnon resonators can be coupled over
macroscopic distances, and using local time-resolved detection, we demonstrate coherent, Rabi-like, energy exchange between them [6]. Conversely, photons in two separate coplanar waveguides can be transmitted in a directional manner via nonreciprocal coupling to magnons [7]. Lastly, I will show how a superconducting qubit can be used for sensitively detecting magnon populations over a broad dynamic range [8]. These measurements illustrate the potential of using magnons for coherently controlled interactions ultimately even in the single quantum limit.


[1] Y. Li et al., J. Appl. Phys. 128, 130902 (2020). [2] D. D. Awschalom et al.,
IEEE Quantum Engin. 2, 5500836 (2021). [3] Y. Li et al., 2022 IEEE Intern.
Electr. Dev. Meeting, 14.6.1 (2022). [4] Z. Jiang et al., Appl. Phys. Lett. 123,
130501 (2023). [5] Y. Li et al., Phys. Rev. Lett. 123, 107701 (2019). [6] M.
Song et al., Nat. Commun. 16, 3649 (2025). [7] Y. Li et al., Appl. Phys. Lett.
123, 022406 (2023). [8] S. Rani et al., Phys. Rev. Appl. 23, 064032 (2025).

Phase transitions in solids are often accompanied by structural changes, but subtle lattice distortions can remain hidden from conventional crystallographic probes, hindering the identification of the correct order parameters. A case in point is Ca3Ru2O7, a correlated polar ruthenate with well-characterized phase transitions, whose ground state structure has recently become a subject of debate. This uncertainty stems from extremely small atomic displacements (~0.001 A) between competing phases, beyond the resolution of X-ray diffraction, neutron scattering, or optical second-harmonic generation. In this work, we propose a method to detect hidden symmetry breaking by leveraging nonlinear transport induced by quantum geometry. We show that Ca3Ru2O7 is a Weyl chain semimetal in both phases. The low-symmetry phase, classified as an altermagnet by symmetry, features distorted topological surface states that are asymmetric along the polar b) axis. However, the nonrelativistic spin splitting is too weak (~ 0.1 meV) to be resolved directly, regarding the altermagnetism. In contrast, Weyl chains generate a large quantum metric at the Fermi surface, leading to nonlinear conductivities that are orders of magnitude stronger in the low-symmetry phase. A longitudinal nonlinear conductivity along the polar axis emerges exclusively in this phase, providing a sensitive probe to qualitatively distinguish it from the high-symmetry structure, which is confirmed by a recent experiment. Our work establishes a route for identifying hidden symmetry breaking in complex quantum materials through the interplay of crystal symmetry, topology and nonlinear quantum transport.

The properties of complex quantum materials (QM), such as transition metal oxides, arise from the interplay of electrons, phonons, and magnons, making them highly sensitive to external parameters like pressure, doping, fields, and temperature. This susceptibility makes QM ideal for experiments where tailored electro-magnetic fields can be used to induce novel properties on ultrafast timescales [1].
I will present our efforts to manipulate material properties through light, both in free space and optical cavities. After reviewing our work on cuprates, which demonstrates the feasibility of light-driven phase control [2–4], I will introduce new spectroscopic methods that merge quantum optics with time-domain techniques to probe fluctuations in non-equilibrium phases [5–11]. 


Building on our recent demonstration that a metal–insulator transition in 1 T – TaS2 can be controlled by resonant cavity coupling [12, 13], I will outline future directions aimed at exploring new light–matter coupling regimes. Our goal is to harness such interactions to bypass thermodynamic limits and dynamically sustain quantum coherence, potentially enabling coherent quantum phases under ambient conditions.


[1] C. Giannetti et al., Advances in physics 65, 58-238, (2016). [2] D. Fausti et
al., Science 331, 189-191 (2011). [3] F. Giusti et al., Phys. Rev. Lett. 122,
067002 (2019). [4] A. Marciniak et al., Nature Physics 17, 368–373 (2021).
[5] F. Randi et al., Phys. Rev. Lett. 119, 187403 (2017). [6] M. Esposito et al.,
New J. Phys. 16, 043004 (2014). [7] M. Esposito et al., Nat. Comm. 6, 10249
(2015). [8] J. O. Tollerud et al., PNAS March 19, 116 (12) 5383-5386 (2019).
[9] J. of Physics B 53, 145502 (2019). [10] F. Glerean et al., Optics Letters 45,
3498 (2020). [11] G. Sparapassi et al., Light: Science and Applications 11, 44
(2022). [12] G. Jarc et al., Nature 622, 487–492 (2023). [13] F. Fassioli et al.,
Phys. Rev. B 111, 165425 (2025).

While topological phases of matter have predominantly been studied for isolated Hermitian systems, a recent shift has been made towards considering these phases in the context of non-Hermitian Hamiltonians. Non-Hermitian topological phenomena reveal an enrichment of the phenomenology of topological phases, and forms a rapidly growing new cross-disciplinary field. In particular, non- Hermiticity plays a central role in both classical and quantum systems. In the classical realm, this
comes about due to, e.g., gain and loss processes in optics, while in the quantum realm, non-Hermiticity describes the dynamics of open quantum systems as well as scattering, decay, broadening and resonances due to, e.g., interactions and disorder. Non-Hermitian Hamiltonians may feature many exotic properties, which are radically different from their Hermitian counterparts, such as the generic appear-
ance of exotic exceptional structures, a break down of the famed bulk-boundary correspondence, and the piling up of bulk states at the boundaries known as the non-Hermitian skin effect. In this talk, I will provide an overview of the field focussing on fundamental aspects, experimental realizations and I will briefly touch upon applications

Altermagnetic materials are characterized by collinear magnetic order with a vanishing net magnetic moment, but nevertheless have a spin-splitting in their non-relativistic electronic band structure [1]. From ab initio calculations we have identified around 60 altermagnetic materials [2]. From a theoretical point of view several physical properties that render altermagnets different from canonical antiferro-, ferro- and ferri-magnets will be discussed [3]. These include certain spin and heat transport features and piezomagnetic responses. By symmetry in principle also an anomalous Hall effect (AHE) is allowed in certain altermagnets. In particular we introduce an altermagnetic model in which the emergence of an AHE is driven by interactions [4]. Quantum Monte Carlo simulations show that the system undergoes a finite temperature phase transition governed by a primary antiferromagnetic order parameter accompanied by a secondary altermagnetic one. The emergence of both orders turns the metallic state of the system, away from half-filling, into an altermagnet with zero net moment but a finite AHE.


[1] C. Li et al., arXiv:2405.14777 (2024).

[2] Y. Guo et al., Materials Today Physics, 32, 100991 (2023).

[3] O. Gomonay et al., npj Spintronics 2, 35 (2024).
[4] T. Sato et al., Phys. Rev. Lett. 133, 086503 (2024).

Frustrated and low-dimensional spin systems show a wealth of different magnetic states depending on the specifics of their internal interactions and on external parameters such as magnetic field, pressure, and doping. They provide a promising avenue for realizing exotic quantum states of matter. The degree of frustration in such materials depends on the detailed exchange interactions as well as on the exact interplay of spin, charge, and orbital degrees of freedom and their coupling to the lattice. By use of high-magnetic-field studies, such as magnetization, electron spin resonance (ESR), nuclear magnetic resonance (NMR), and ultrasound investigations, we gained important information on the magnetic exchange and on the spin-phonon coupling. Here, I will present some selected pulsed-magnetic-field studies of frustrated magnetic materials that host a broad range of remarkable quantum phases. For the triangular-lattice antiferromagnets Cs2CuBr4 and Cs2CuCl4, for example, high-field ESR data provided exact and conclusive information on the exchange couplings in these frustrated spin systems. For Cs2CuCl4, we can tune these exchange couplings and the degree of frustration by applying pressure. Equally captivating are low-dimensional spin-chain materials, such as the frustrated spin-1/2 chain compound LiCuVO4, for which we found thermodynamic and microscopic evidence for a spin-nematic state. For the Ising spin-1/2 chain compound BaCo2V2O8, we found high-field quantum criticality as well as exotic magnon excitations in a transverse magnetic field. Finally, our microscopic studies, using x-ray magnetic circular dichroism, allowed resolving the spin structures in MnCr2S4. For this spinel compound the magnetic exchange between Mn and Cr leads to an ultra-robust magnetization plateau in magnetic fields and a rich phase diagram with realizations of so-called supersolid phases.

Muon spin rotation/relaxation (μSR) is a powerful technique to investigate the local magnetical properties of materials showing magnetism and/or superconductivity. In particular, its unique time window for the observation complementary to other microscopic techniques has brought valuable information in elucidating the microscopic details of quantum magnetism. In this talk, a Kitaev quantum spin liquid (QSL) candidate H3LiIr2O6 is highlighted as a recent example to which μSR has been applied to address the dynamical scaling of the spin fluctuations, and point to the finite density of states with the form
N (E) ∼ E−ν , which is expected for the Kitaev QSL in the presence of vacancies.

The recent Kitaev model (2006) provides an exact model to achieve a quantum spin liquid ground state in a 2D honeycomb lattice system through Ising-like bond- dependent interactions [1]. While first considered as a toy model, a theoretical work from Jackeli and Khaliullin has paved the way towards the realization of Kitaev physics in bulk materials. They first showed that bond-dependent interactions can be achieved through the interplay between crystal field, spin-orbit coupling and bond geometry using 4d and 5d transition metal ions, that exhibit a strong spin- orbit coupling [2]. Since then, a significant amount of experimental works have focused on iridate and ruthenate compounds to find suitable candidate materials. Co2+ ions have been recently put forward for realising Kitaev interactions [3,4,5], a prediction we have tested by investigating the magnetic properties and spin dynamics in several cobalt honeycomb lattice compounds [6]. In particular, the ground state and Hamiltonian of the honeycomb lattice material BaCo2(AsO4)2 hosting magnetic Co2+, have been debated for decades [7,8]. To investigate the relevance of bond-dependent Kitaev-like interactions in this material, we have combined magnetization, ac-susceptibility and neutron scattering measurements on a BaCo2(AsO4)2 single-crystal, together with advanced modeling. Our experimental results highlight a collinear magnetic ground state with intrinsic disorder associated to an average incommensurate propagation vector. Monte Carlo simulations and linear spin wave calculations were performed to obtain a spin model compatible with this unusual ground state, the dispersion of magnetic excitations and a magnetization plateau under magnetic field. We thus show that bond-dependent anisotropic interactions, including Kitaev-like interactions, are necessary to account for the puzzling properties of this long-explored material, and are hence a general ingredient in the cobaltates [9].


[1] A. Kitaev, Annals of Physics, 321, 2-111 (2006).

[2] G. Jackeli and G. Khaliullin, Phys. Rev. Lett., 102, 017205 (2009).

[3] H. Liu and G. Khaliullin, Phys. Rev. B, 97, 014407 (2018).

[4] R. Sano et al, Phys. Rev. B, 97, 014408 (2018).

[5] H. Liu, J. Chaloupka and G. Khaliullin, Phys. Rev. Lett., 125, 047201 (2020).

[6] M. Songvilay et al., Phys. Rev. B, 102, 224429 (2020).

[7] L.-P. Regnault et al., Physica, 86-88B, 660 (1977).

[8] L.-P. Regnault et al., Heliyon, 4, e00507 (2018).

[9] A. Devillez et al., arXiv:2503.22300 (2025).

Infrared and THz magneto-spectroscopy are powerful experimental tools for studying various classes of topological materials. These techniques offer relevant insights into the electronic band structures of diverse topological crystals and are also frequently used to explore intriguing relativistic-like phenomena. In my talk, I will review recent progress in the field of infrared magneto-spectroscopy applied to topological materials and discuss selected results, including both in-house and collaborative research conducted at the high-field facilities in Grenoble’s laboratory. These investigations encompass: (i) bulk and surface states in three-dimensional
topological insulators (Sb2Te3 [1], ZrTe5 [2], and BiSbTe2S [3]), with the latter showing peculiar cyclotron resonance absorption on surface electrons visible up to room temperature; (ii) magnetic dichroism induced by the Berry curvature in the antiferromagnetic topological insulator MnBi2Te4 [4]; (iii) the optical band gap in a dispersive nodal-line in the NbAs2 Dirac semimetal, whose angle-dependence can be interpreted in terms of a Lorentz-boost-driven renormalization [5]; and (iv) the alleged magnetic Weyl semimetal EuCd2As2 [6].


[1] I. Mohelsky et al., Phys. Rev. B 109, 165205 (2024).

[2] I. Mohelsky et al., Phys. Rev. B 107, L041202 (2023).

[3] I. Mohelsky et al.,  rXiv:2504.08420 (2025).

[4] S.-K. Bac et al., Phys. Rev. Lett. 134, 016601  (2025).

[5] J. Wyzula et al., Adv. Sci. 9, 2105720 (2022).

[6] D. Santos-Cottin et al., Phys. Rev. Lett. 131, 186704 (2023).

TBA

TBA

Strongly correlated electron systems exhibit quasiparticles with effective masses that are often enhanced by orders of magnitude relative to their band values, reflecting the intricate interplay of Coulomb interactions, spin fluctuations, and hybridization. Terahertz (THz) spectroscopy in very high magnetic fields can provides a unique, phase-coherent probe of these renormalized masses via direct ac-
cess to the low-energy electrodynamics and field-induced cyclotron resonances. In this work, time-domain THz experiments are employed to measure frequency- and field-dependent complex conductivities in correlated systems ranging from heavy fermion compounds to cuprate superconductors. Analysis of cyclotron resonance shifts and linewidths allows precise determination of quasiparticle effective masses, while simultaneously revealing the evolution of inelastic scattering as a function of
field. We present recent results from optical spectroscopy on two classes of correlated metals: cuprate high-temperature superconductors and the heavy-fermion compound CeCoIn5. Using time-domain terahertz spectroscopy in high magnetic fields, we have observed cyclotron resonance in optimally doped La2-xSrxCuO4, opening a new route to study quasiparticle dynamics in the cuprates. Measurements across a wide doping range (x = 0.13–0.26) reveal a systematic increase in the cyclotron mass mc, reaching values exceeding 13 me. This trend contrasts sharply with masses inferred from heat capacity, which peak near the pseudogap critical point p∗ and/or Lifshitz transitions. Remarkably, despite ARPES evidence for a Lifshitz transition in this doping range, we find no divergence in mc near p∗
or the topological change of the Fermi surface, demonstrating that any associated singularities are too weak to affect the cyclotron mass. In parallel, we have investigated thin films of the heavy fermion CeCoIn5 in large magnetic field. The complex optical conductivity, analyzed within Drude and extended Drude frameworks, reveals the formation of a narrow Drude-like peak below the ∼ 40 K Kondo coherence temperature due to f –conduction electron hybridization. The peak width exhibits T2 scaling over a large field range up to 25 T, providing spectroscopic evidence for a hidden Fermi-liquid state in this prototypical heavy-fermion material. Together, these studies establish high-field THz spectroscopy and optical conductivity as powerful probes of quasiparticle mass renormalization and coherence in strongly correlated materials.

The properties of electrons in solids are fundamentally characterized by two essential features: a band dispersion (the eigenvalues of the Bloch Hamiltonian as a function of momentum and spin) and an extended wavefunction (the eigenstates of
the Bloch Hamiltonian). The quantum geometric tensor (QGT), composed of the quantum metric and Berry curvature, quantifies certain geometrical properties of the electron wavefunctions that are key to understand collective phenomena such as the quantum Hall state, ferroelectricity, and various optical responses. While QGT measurements have been reported for engineered two-level systems, probing it in solids remains challenging due to the limitations of conventional spectroscopy, which primarily targets band dispersion.


In this talk, I will introduce a novel method to estimate the QGT in solids using photon polarization and electron spin-resolved angle-resolved photoemission spectroscopy (ARPES). By measuring the momentum-resolved mass and orbital angular momentum of Bloch wavepackets, we can effectively determine the quantum metric and (spin) Berry curvature through auxiliary observables [1]. This approach, applicable to any crystalline solid, provides access to properties arising from non-trivial band characteristics, including nonlinear responses and Chern numbers, demonstrating the potential of this technique to advance our understanding of quantum geometry in solids.


[1] M. Kang et al., Nature Physics 21, 110 (2025).

I will introduce a model of an active quantum particle and discuss its properties. The particle has a set of internal states that mediate exchanges of heat with external reservoirs. Heat is then converted into motion by means of a spin-orbit term that couples internal and translational degrees of freedom. The quantum features of the active particle manifest both in the motion and in the heat-to-motion conversion.
Furthermore, the stochastic nature of heat exchanges impacts the motion of the active particle and fluctuations can be orders of magnitude larger than the average values. The combination of spin-orbit interaction under non-equilibrium driving may bring active matter into the realm of cold atomic gases where our proposal can be implemented.


[1] A.-G. Penne et al., arXiv:2503.07751 (2025).

In magic angle twisted bilayer graphene, transport, thermodynamic and spectroscopic experiments pinpoint to a competition between distinct low-energy states
with and without electronic order, as well as a competition between localized and delocalized charge carriers.


In this talk I will discuss these observation in the context of a heavy fermion-like description. We will show [1-3] through a combination of Hartree-Fock and
Dynamical Mean Field Theory that such a heavy fermion picture is able to describe in a unified way many of the experimentally observed complex orders in these materials.


[1] Hu et al., Phys. Rev. Lett. 131, 166501 (2023).

[2] Rai et al., Phys. Rev. X
14, 031045 (2024).

[3] Kim et al., arXiv:2505.17200 (2025).

Optical probes are naturally well suited to detecting broken symmetries, including time-reversal symmetry (T), and are frequently used in this way, for example, to map ferromagnetic domains. But the conditions under which optics can detect T – breaking in antiferromagnets with no net magnetization are far more subtle. The key distinction is whether the effect of T can be undone by a simple translation (τ1/2); if it can, the product T τ1/2 is a symmetry of the system and T -breaking is usually invisible to bulk probes. In contrast, antiferromagnets that do not preserve T τ1/2 display a range of T -breaking phenomena, such as the magnetoelectric and piezomagnetic effect. But what exactly does “bulk” mean? And more specifically, are optical probes “bulk”: can they detect T -breaking in T τ1/2 -invariant antiferromagnets? We address these questions by directly comparing two antiferromagnets: EuIn2As2 that breaks in T τ1/2 and MnBi2Te4 that does not. In the first case, we show how an unconventional optical probe, linear magneto-birefringence, can reveal symmetry breaking invisible to more standard measurements. In the second, we demonstrate how perhaps the most standard optical probe of magnetism, reflection circular dichroism, can in fact detect antiferromagnetism even when T τ1/2 is preserved. Together, these experiments demonstrate both the power and the versatility of optics as a probe of symmetry breaking in quantum materials.

TBA

Temporal modulation of the Berry phase in a condensed matter can produce the emergent electric field acting on conduction electrons. For example, conducting multiferroics, such as semi-magnetic topological insulators and polar ferromagnetic Weyl semimetals, in which the electronic polarity (P) and the ferromagnetic order (M) coexist, can generate the emergent electric field as a consequence of the temporal drive of the toroidal moment (T ∼ P M). One other example for the emergent electric field generation is the temporal drive of the emergent magnetic field (Berry curvature) as typically observed in the current drive of the magnetic skyrmion lattice. For more general example, the spin chiral matter in the real space can be always driven by ac electric current to generate the emergent electric field. All these can be termed emergent electromagnetic induction as an extension of Faraday’s law in classic electromagnetism. Such emergent electromagnetic induction based on the spin chiral matter is applied to the design of nanometric inductor or sensor element.


Here, several mechanisms of emergent electromagnetic induction arising from the
real space and momentum space spin topology are discussed together with the
experimental observations for the large emergent electric field generation in topo-
logical magnets

The thermal Hall effect (THE) in magnetic insulators has been widely investigated, yet its underlying mechanism remains debated. Arguably the most renowned example of planar THE was reported in candidate Kitaev material- α-RuCl3. However, its origin remains under intense debate with proposed mechanisms including Majorana edge modes [1], topological magnons [2], and phonons [3]. Here, we study Na3Co2SbO6 (NCSO) as an ideal reference system to α-RuCl3, owing to its similar
lattice structure and magnetic ground state in zero field [4-6]. Upon application of magnetic fields, NCSO rapidly enters a fully-polarized state rather than a paramagnetic state from a zigzag AF ordered state, excluding the possibility of the Kitaev physics and the resultant Majorana edge modes in contrast to α-RuCl3. Although only magnons and phonons are available as the heat carriers, we observe a sizable planar thermal Hall signal (κxy ) in the field-induced fully polarized state of NCSO, which is comparable to that of α-RuCl3 with the same field angle anisotropy [7]. κxy is suppressed at the lowest temperatures, indicating their bosonic origin. While topological magnons yield a finite THE, the experimentally observed magnitude of κxy is larger than the theoretical prediction [8]. With increasing the magnetic field and hence the magnon gap, we do not see the rapid decay of κxy expected for those purely from topological magnons. We combine these experimental signatures and constraints and propose the possible magnon-phonon drag as the underlying mechanism in which highly mobile phonons enhance THE driven by topological magnons in particular at high fields.


[1] Y. Kasahara et al., Nature 559, 227–231 (2018).

[2] P. Czajka et al., Nat. Mater. 22, 36–41 (2023).

3] É. Lefran¸cois et al., Phys. Rev. X 12, 021025 (2022).

[4] S. Kim et al., Phys. Rev. B 109, L140101 (2024).

[5] E. Vavilova et al., Phys. Rev. B 107, 054411 (2023).

[6] J.-Q. Yan et al., Phys. Rev. Mater. 3, 074405 (2019).

[7] T. Yokoi, et al., Science 373, 568–572 (2021).

[8] L. E. Chern, et al., Phys. Rev. Lett. 126, 147201 (2021).

Deconfined quantum criticality (DQC) describes continuous phase transitions beyond the Landau-Ginzburg paradigm with emergent fractionalized quasiparticles. A paradigmatic example is the continuous transition between a valence bond solid (VBS) and Neél ordered phase in low-dimensional frustrated antiferromagnets. Since the VBS order parameter breaks lattice symmetries, it may couple to lattice distortions (phonons) at appropriate momenta.


A field-theoretical study suggested that treating the phonons as static lattice distortions induces an instability towards a distorted lattice, rendering the transition
strongly first-order [1]. In contrast, a full quantum treatment predicts that DQC persists above a critical phonon frequency.


In our work, we investigate the stability of DQC under spin-phonon coupling in a one-dimensional anisotropic J1 − J2 model using large-scale tensor network simulations. For static lattice distortions, we confirm that the coupling generally drives the Neél-VBS transition towards strong first-order character. Within a full
quantum treatment, we investigate the character of the transition depending on phonon frequency. We identify the regime where the transition remains second-
order and extract the corresponding critical exponents. We further compute the dynamical phonon spectral function, which provides insight into the nature of the
spin-phonon coupling and provides further evidence for the stability of DQC in the quantum regime.


[1] D. Hofmeier et al., PRB 110, 125130 (2024).

Strange metallicity with T-linear electrical resistance, preceding high-Tc superconductivity is an enigmatic, yet crucial, signature of correlation physics. We study the hydrostatic pressure dependence of ferromagnetism in the kagome metal CrNiAs by electrical transport and magnetization measurements up to 25 GPa [1]. In contrast to other kagome ferromagnets, a linear suppression of the Curie temperature
is found, resulting in a ferromagnetic quantum critical point at a critical pressure pc ∼ 12 GPa. Remarkably, from pc up to the maximal measured pressure, a broad strange metal phase arises, which at low temperatures can be converted to a Fermi liquid in applied magnetic field, phenomenologically described by a zero-field quantum critical line in the T –p phase diagram. This establishes pressurized kagome ferromagnets as an intriguing platform for strange-metal behavior.


[1] B. Shen et al., arXiv:2503.09524 (2025)

In cubic chiral magnets, the efficient coupling of magnetic skyrmion lattices to spin currents and magnetic fields permits their dynamical manipulation. When placed in a magnetic field with a slowly oscillating direction, the skyrmion lattice can be depinned, realizing a non-equilibrium state with vanishing depinning currents. With the combination of oscillating magnetic fields and applied electric currents, we explore a rich non-equilibrium phase diagram characterized by distinct stages of skyrmion lattice unpinning. We propose an effective slip–stick model for the bending and motion of the skyrmion lines in the presence of disorder, which reproduces key features observed in transverse susceptibility and time-resolved small-angle neutron scattering measurements and describes the existence of several dynamical skyrmion lattice phases under shaking and pushing, representing new phases of
matter far from thermal equilibrium.

The kagome network hosts a plethora of interesting quantum phenomena, ranging from topological bandstructures to superconducitivity and quantum spin liquids. Although the emergence and tunability of these states by external forces has been
widely predicted theoretically, the experimental verification remains a challenge, largely due to the difficulty to combine many spectroscopic techniques with strong stimuli. In this project, we show the versatility of optical spectroscopy in first iden-
tifying the optical fingerprints of these unusual states of the electronic structure, and later monitor their changes under e.g. pressure or external fields. Along this line, we reveal the sensitivity of the electronic band structure of kagome FeGe to hydrostatic pressure at room temperature, we compare the influence of chemical and mechanical pressure on the nodal line in Co3Sn2S2, and we trace the magnetic field induced reconstruction of hybridized 4f bands in the non-collinear antiferromagnet HoAgGe. These results highlight the versatility of emergent phenomena on the kagome lattice and their efficient manipulation in accessible pressure and field regimes.

Spin ice systems represent a prime example of constrained spin systems and exhibit rich low-energy physics. In this talk, we explore how introducing a tunable anisotropic spin coupling to the conventional Ising spin ice Hamiltonian on the breathing pyrochlore lattice affects the ground state properties of the system. We find significant changes in the ground state structure, reflected in characteristic
modifications of the spin structure factor and in a reduction of residual entropy at low temperatures. Focusing on one limit of the resulting phase diagram, we will analyze how a small perturbation in a magnetically frustrated system can drive dimensional decoupling and give rise to unconventional excitations

We investigate the Faraday effect of magnon-polaron hybrid modes in the polar altermagnet candidate Fe2Mo3O8 using time-resolved THz spectroscopy (TDS- THz). The frequency region between the hybrid modes split by the magnetic field yields the strongest Faraday rotation of up to 103,◦ in a field of 4 T. In case of strong coupling to the light field, linewidth and oscillator strength of the excitations usually cannot be precisely extracted by frequency-domain methods and estimates of the Faraday response become difficult. By analyzing the polariton time-domain signal directly with the time trace of a Lorentz oscillator, we successfully capture the complex transmission tensor components with high accuracy and can reliably extract magnetic circular dichroism and Faraday rotation values.

We analyze the quantum geometric contribution to the intrinsic second-order nonlinear Hall effect (NLHE) for a general multiband Hamiltonian. The nonlinear conductivity, obtained in Green’s function formalism, is decomposed into its quantum geometric constituents using a projector-based approach. In addition to the Berry curvature and interband quantum metric dipoles, previously identified in semiclassical calculations, we obtain a third term of quantum geometric origin, given by the momentum derivative of the intraband quantum metric. This contribution provides substantial corrections to the NLHE in topological magnets and becomes particularly large in topological antiferromagnets with gapped Dirac cones. Through a symmetry classification of magnetic space groups, we identify several candidate materials that may exhibit large intrinsic NLHE, including the antiferromagnets Yb3Pt4, CuMnAs, and CoNb3S6, as well as the nodal-plane material MnSi.

We demonstrate the reversible electrical manipulation of magnetiusm in a 2- dimensional WTe2/Fe3GeTe2 (FGT) bi-layer with reduced thickness. By pushing a charge current I in ultra-thin WTe2, an unconventional z-polarized spin accumulation is generated via the Berry curvature dipole. The spin polarized electrons act on the adjacent FGT with perpendicular anisotropy and leads to a strong modification of the anomalous Hall effect (AHE) and Curie temperature. Further study shows that the effect vanishes for pure FGT, and the modifications become weaker for thicker FGT films, indicating the modification is an interfacial effect. We propose that the z-polarized spin current modifies the exchange splitting of FGT [1], which leads to a modification of the Berry curvature and affects the AHE in a nontrivial way. The electrical control of AHE by the z-polarized spin current in van der Waals perpendicular magnet shows potential applications for next-generation spintronic devices and opens doors for future control of quantum magnets.


[1] L. Chen. et al., Nature, 633, 548-553 (2024).

While the origin of long-range magnetic orders can be found on the scale of the crystallographic unit cell in the nanometer range, their phenomena are visible far beyond this, up to the micrometer scale. The causes of magnetic orderings are as diverse as the magnetic textures that occur, ranging from stripes and bubbles to topologically non-trivial objects such as merons, skyrmions, and Bloch points and magnetic edge states. Due to the close coupling of the micro and nanoscale, magnetic textures in many cases allow far-reaching conclusions to be drawn about the usually difficult-to-access details of magnetic order.


In our presentation, we discuss the magnetic, non-collinear textures revealed by magnetic force microscopy (MFM) in two inter-metallic compounds with a kagome structure: On TbMn6Sn6, in which topological features have been observed in real and reciprocal space, we investigate the spin reorientation transition at approximately 315 K and identify an intermediate state that suggests an unusual arrangement of magnetic anisotropies. Secondly, the magnetic phases on HoAgGe below 4 K, whose topological, magnetic structure on the unit cell level is under current debate, and their coexistance are explored to determine the micro-magnetic couplings within the three-dimensional kagome stack. By varying the temperature, magnetic field, and sample geometry, we derive conclusions about the stability of the magnetic phases under consideration. Our findings underline the potential of MFM for magnetic texture recognition that can be understood intuitively and impressively as part of the outreach project.

Recently, A. Hellenes et al. proposed metallic state with p-wave spin splitting of electronic bands, yet without the need for a correlation-driven Pomeranchuk in-
stability [1]. We demonstrate the experimental realization of an antiferromagnetic metal satisfying the symmetry requirements for p-wave spin polarization in momentum space, based on X-ray and neutron scattering experiments. We further fabricate mesoscopic devices which allow for the study of emergent anisotropic transport in such p-wave magnets.


[1] A. Hellenes et al., arXiv:2309.01607 (2025).

Geometrical frustrated Skyrmion lattices exemplify nontrivial topological states with non-zero scalar spin chirality and a finite Berry curvature in real space. In
2019, T. Kurumaji et al. reported a large topological Hall effect in the skyrmion phase in Gd2PdSi3 related to the spin chirality of the ground state [1]. In this
talk, I will present the thermal Hall conductivity of the frustrated triangular-lattice magnet Gd2PdSi3. Entering the skyrmion lattice ground state causes the field-
dependent thermal Hall effect to sharply increase compared to adjacent incommensurate phases, similar to the behaviour of electric Hall conductivity. Eventually, I investigate the relationship of Hall entropy to the charge current, which reveals a loss-less topological quantum transport in the Skyrmion host Gd2PdSi3.


[1] Takashi Kurumaji et al., Science 365, 914–918 (2019).

Correlated materials with multiple active d orbitals attract intense research interest, as epitomized by unconventional superconductors. In such systems, valence  electrons distribute over multiple energy bands and Fermi surfaces, making it challenging to capture their mutual interactions. Research has therefore largely focused on the ground state and low-energy fermionic excitations near the Fermi level. Here, we use inelastic photon scattering to probe spin-orbit excitations in the correlated metal Sr2RhO4, a 4d-multiorbital system known for its sharp Fermi surfaces. Using polarization-resolved Raman spectroscopy, we observe well-defined yet unconventional excitations around 230 meV with A1g and B1g symmetries [1], analogous to those recently discovered in the well-studied Mott insulators Sr2IrO4 and α-RuCl3. Using a theoretical model based on single-ion picture, we assign them as excitonic transitions between the spin-orbit multiplets J = 1/2 and J = 3/2 of Rh ions (termed as spin-orbit exciton), which is a direct signature of unquenched spin-orbit coupling. Besides, we further performed resonant inelastic x-ray scattering at the Rh L-edge [2] to confirm the collective, propagating character of this excitation, and to study its dispersion in momentum space. Our study reveals well-defined atomic multiplet excitations around 230 meV in correlated metal Sr2RhO4. These spectral features is complement to prior ARPES studies of coherent quasiparticles near the Fermi level, demonstrating that incoherent, atomic-like excitations can coexist with coherent fermionic quasiparticles in multiorbital metals. The discovery of such atomic-scale electronic  excitations in a clean d-electron metal opens up a rich source of information on electronic correlations in metallic systems.
List of posters

Travel Information

The TRR360 International Conference will take place at the hotel of the Ettal Monastery in Ettal in the beautiful Alps.

Klosterhotel Ettal

Kaiser-Ludwig-Platz 10-12

82488 Ettal

The hotel can be reached via car or public transport.

Via public transport:

To reach Ettal with public transport a train must be taken to München-Pasing and there the RB6 or RB60 to Garmisch-Patenkirchen can be taken to the train station Oberau.

 

In Oberau a public bus goes directly to the Klosterhotel in Ettal. The stop is called “Klostergasthof, Ettal”. The local bus runs until 18:55 on Sunday and 19:55 on weekdays. If you arrive later, please contact Ina (ina-marie.pietsch@uni-a.de) so that a taxi can be arranged for you!

 

Advisory Board

Prof. Dr. István Kézsmárki (University of Augsburg)

Prof. Dr. Philipp Gegenwart (University of Augsburg)

Prof. Dr. Christine Kuntscher (University of Augsburg)

Prof. Dr. Markus Heyl (University of Augsburg)

Prof. Dr. Hidenori Tagaki (MPI for solid-state research)

Dr. Eva Benckiser (MPI for solid-state research)

Prof. Dr. Frank Pollmann (TU Munich)

Prof. Dr. Christian Pfleiderer (TU Munich)

Prof. Dr. Michael Knap (TU Munich)

Prof. Dr. Johannes Knolle (TU Munich)

Prof. Dr. Alexander Tsirlin (University of Leipzig)

Prof. Dr. Bernhard Keimer (MPI for solid-state research)

Local Organizers

Angela Sarafimovska (University of Augsburg)

Dr. Ina-Marie Pietsch (University of Augsburg)

Dr. Lilian Prodan (University of Augsburg)

Dr. Franz Mayr (University of Augsburg)

PD Dr. Hans-Albrecht Krug von Nidda (University of Augsburg)

André Deyerling (TU Munich)

Josef Willsher (TU Munich)