
chair: Masafumi Udagawa

09:00  09:20

Nic Shannon
(Okinawa Institute of Science and Technology Graduate University)
Fractional excitations on the pyrochlore lattice, from PKS late 2000 to the present …

09:20  09:40

Wolfram Brenig
(Technische Universität Braunschweig)
Finite temperature dynamics of Kitaev magnets"
Electronic correlations can lead to highly entangled states of quantum matter in which electrons and spins are fractionalized into nonlocal novel elementary excitations. Quantum spin liquids (QSLs) in frustrated magnets are among such states and represent a timely field of search for manifestations of fractional quasiparticles. Here we will report on some of their fingerprints in transport and spectroscopy in Kitaev magnets, which are among the QSLs of great current interest, comprising a compass Ising model on the honeycomb lattice, allowing for fractionalization of spins into mobile Majorana matter and gauge flux visons.

09:40  10:00

MingChiang Chung
(National Chung Hsing University)
Phase prediction of 1D spin1 bilinearbiquadratic models by using spinspin correlation functions and unsupervised learning
In this talk, we report the progress of predicting four different phases (Haldane, Dimerized, Ferromagnetic, and critical phases) of 1D spin1 BilinearBiquadratic models by using unsupervised learning. The difficulty of detecting a secondorder phase transition point is overcome by using three spinspin correlation functions.

10:00  10:20

Ora EntinWohlman
(Tel Aviv University)
Thermoelectric performance of nano junctions subjected to microwave driven spinorbit coupling
Coherent charge and heat transport through periodically driven nanodevices provide a platform for studying thermoelectric effects on the nanoscale. Here we study a junction composed of a quantum dot connected to two fermionic terminals by two weak links. An AC electric field induces timedependent spinorbit interaction in the weak links. We show that this setup supports DC charge and heat currents and that thermoelectric performance can be improved, as reflected by the effect of the spinorbit coupling on the Seebeck coefficient and the electronic thermal conductance. Our analysis is based on the nonequilibrium Keldysh Green's function formalism in the time domain and reveals an interesting distribution of the power supply from the AC source among the various components of the device.

10:20  10:40

Shivaji Sondhi
(University of Oxford)
Continuum fractons
I will outline a set of results on the classical and quantum mechanics of fractons—particles defined by a consistent set of multipole conservation laws. I will demonstrate that the nonlinear, Machian dynamics of fractons are characterized by latetime attractors in positionvelocity space, despite the absence of attractors in phase space as dictated by Liouville's theorem. These attractors violate ergodicity and lead to nonequilibrium steady states, which invariably break translational symmetry, even in spatial dimensions where the HohenbergMerminWagnerColeman theorem for equilibrium systems forbids such breaking. I will also discuss progress in quantizing this system.

10:40  11:10

group photo (to be published on the event website) & coffee break


chair: Revaz Ramazashvili

11:10  11:30

Walter Metzner
(Max Planck Institute for Solid State Research)
Pseudogap in the twodimensional Hubbard model: gauge theory for fluctuating magnetic order
The pseudogap phase in cuprate superconductors is one of the most intriguing challenges in the theory of high temperature superconductivity. In this talk we elaborate on the idea that pseudogap phenomena are mostly due to strong magnetic fluctuations. Using the twodimensional Hubbard model to describe the electrons in the copperoxygen planes of the cuprates, a gauge theory of fluctuating magnetic order is formulated and analyzed [1]. The theory is based on a fractionalization of electrons in fermionic chargons with a pseudospin degree of freedom and bosonic spinons, which leads to a SU(2) gauge redundancy. The chargons undergo Neel, spiral, or stripe order below a density dependent transition temperature $T^*$. Fluctuations of the spin orientation are described by a nonlinear sigma model obtained from a gradient expansion of the spinon action. The spin stiffnesses are computed from a renormalization group improved random phase approximation. The spinon fluctuations prevent magnetic longrange order of the electrons at any finite temperature. The phase with magnetic chargon order exhibits many features characterizing the pseudogap regime in highTc cuprates: a strong reduction of charge carrier density, a spin gap, and Fermi arcs. A substantial fraction of the pseudogap regime exhibits electronic nematicity.
[1] P. M. Bonetti and W. Metzner, Phys. Rev. B 106, 205152 (2022).

11:30  11:50

Sergej Flach
(Institute for Basic Science, Daejeon)
Electronic correlations: from incremental expansions for Hubbard systems to many body flatband physics

11:50  12:10

David Campbell
(Boston University)
Multiscale functional renormalization group approach to the 1D extended Hubbard model
We review our recent development of the Multiscale Functional Renormalization Group (MfRG) as an approach to the study of strongly correlated electronic materials in which both electronelectron (ee) and electronphonon (eph) interactions play important roles. Our MfRG method includes in a systematic manner the effects of the scattering processes involving electrons away from the Fermi surface and also permits proper inclusion of phonon retardation effects. After introducing the basic concepts, I will discuss in detail the application of this method to the 1D Extended Hubbard model and show that it correctly captures the subtle bondorder wave (BOW) phase in that model.
We will then discuss additional applications of the MfRG method and show that it can be applied to multiband models in higher dimensions, recovering previously known results and predicting novel behaviors that have been seen in experiment. Finally, we will discuss possible future applications of the MfRG approach.

12:10  12:30

Balázs Dora
(Budapest University of Technology and Economics)
Anomalous correlations at exceptional points
We consider a PTsymmetric Fermi gas with an exceptional point, representing the critical point between PTsymmetric and symmetry broken phases. The low energy spectrum remains linear in momentum and is identical to that of a hermitian Fermi gas. The fermionic Green's function decays in a power law fashion for large distances, as expected from gapless excitations, albeit the exponent is reduced from 1 due to the quantum Zeno effect. In spite of the gapless nature of the excitations, the ground state entanglement entropy saturates to a finite value, independent of the subsystem size due to the nonhermitian correlation length intrinsic to the system. Attractive or repulsive interaction drives the system into the PTsymmetry broken regime or opens up a gap and protects PTsymmetry, respectively.

12:30  14:00

lunch


chair: Mike Zhitomirsky

14:00  14:20

Klaus Richter
(Universität Regensburg)
Dealing with the exponentialwall problem for manybody systems
Starting with Peter Fulde's late works addressing the exponentialwall problem for large particle numbers, I will discuss loosely related approaches we have developed to
approximately compute the smoothed density of states of certain manybody systems. Because of the vast growth of the manybody level density with excitation energy,
its smoothed form is of central relevance for spectral and thermodynamic properties of interacting quantum systems. Our method provides predictions for excitation spectra
that enable access to finitetemperature thermodynamics in large parameter ranges. Another application concerns manybody scattering through interacting media due to a
fundamental relation between the smooth level density and the average dwell time.

14:20  14:40

Natasha Kirova
(Université ParisSaclay)
Effects of electronic correlations in optically active polymers
Optically active polymers are intensively studied because of their optical properties, promising applications in light emitting and in energy harvesting. Still, there is no consensus on the very nature of the light emitting excitons. We develop an approach considering the polymers as generic one dimensional semiconductors with specific features of strongly correlated electronic systems. We demonstrate that optics of polymers can be understood within this combined frame of long range Coulomb interaction together with strong intramonomer electronic correlations. Theory predicts different kinds of weakly and strongly bound excitons, in singlet and triplet states; all of them already show up in experiments. We shall mention also new polymers with a degenerate ground state which demonstrate solitons with expecting noninteger charge. These systems are promising in search of ferroelectricity in polymers.

14:40  15:00

Kurt Fischer
(National Institute of Technology, ShunanShi)
Mean field approximation applied to number theory
The meanfield approximation provides a simple approach for many models of correlated particles on lattices.
It replaces the original finite dimensional lattice with a generalized multidimensional version, in the infinite dimensional limit.
The same approach sometimes works for zeta functions defined in terms of integers on lattices.
We show how these zeta functions simplify in the infinite dimensional limit.

15:00  15:20

Stefan Kettemann
(Constructor University Bremen gGmbH)
Synchronization of tunneling systems and the magneto sensitivity of low temperature properties of glasses  25 years later
Experiments on the low temperature properties of multicomponent
glasses revealed in 1998 evidence for a phase transition to a
phase with strongly enhanced magnetosensitivity[1].
In the experimental paper [1] and in a theoretical investigation, initiated by Peter Fulde[2], it was suggested that this indicates a transition to a a coherent macroscopic quantum state of coupled tunneling systems.
Here we review the status of the theory of quantum phase transitions in
coupled tunneling systems, and whether
the surprising transition to a phase with strongly
enhanced magnetosensitivity discovered
in the low temperature electric permittivity of multicomponent glasses
can indeed be due to
a quantum phase transition
to a phase, where mesoscopically or even macroscopically large numbers of tunneling systems are coupled by the interaction and
start tunneling in synchrony, yielding a strongly enhanced diamagnetic response as suggested in Ref. [2].
With the recent progress in understanding in long range interacting disordered quantum spin systems
we aim to address this problem again, and review recent evidence for a
Large Spin fixed point in such systems, which might
provide the theoretical foundation for explaining the experimental results of Ref. [1], and thereby confirm the insightful intuition by Peter Fulde
as revealed and developed
in intensive discussions
with the experimentalist Peter Strehlow
and the author 25 years ago.
[1] P. Strehlow, C. Enss, S. Hunklinger, Evidence for a phase transition in glasses at very low temperature: a macroscopic quantum state of tunneling systems?, Phys. Rev. Lett. 80, 5361 (1998).
[2] S. Kettemann, P. Fulde, P. Strehlow, Correlated Persistent Tunneling Currents in Glasses, Phys. Rev. Lett. 83, 4325 (1999).

15:20  15:40

Bernhard Mehlig
(University of Gothenburg)
Correlation hole in correlated random walks
We all remember Peter's explanation of the correlation hole. I want to talk about the correlation hole that shows up in spatial patterns formed by correlated random walks [1]. I want to connect this to recent model calculations that help us to understand the spatial patterns formed by particles in turbulence [2]. I'll go rather quickly from $\hbar \neq 0$ to $\hbar = 0$.
[1] Wilkinson & Mehlig, Phys. Rev. E 68 (2003) 040101
[2] Bec, Gustavsson & Mehlig, Annu. Rev. Fluid. Mech. 56 (2024) 189213

15:40  16:10

coffee break


chair: Debmalya Chakraborty

16:10  16:30

Natalia Perkins
(University of Minnesota, Minneapolis)
Exploring quantum spin liquids: from theory to experiment

16:30  16:50

Ilya Eremin
(RuhrUniversität Bochum)
Spin waves and magnetic skyrmionic textures in proximity to a superconductor: vortexskyrmion interaction, Meissner currents, and ‘superluminal’ propagation of composite modes
Topological spin configurations in proximity to a superconductor have recently attracted great interest due to the potential application of the former in spintronics and as another platform for realizing nontrivial topological superconductors. Their application in these areas requires precise knowledge of the existing exchange fields and/or the stray fields, which are therefore essential for the study of these systems.
In this talk we will analyse theoretically a hybrid heterostructure with magnetic textures including skyrmions inside a chiral ferromagnet interfaced by a thin superconducting film via an insulating barrier. We find that Pearl vortices (PV) are generated spontaneously in the superconductor within the skyrmion radius, while antiPearl vortices (PV) compensating the magnetic moment of the Pearl vortices are generated outside of the Sk radius, forming an energetically stable topological hybrid structure. Finally, we analyze the interplay of skyrmion and vortex lattices and their mutual feedback on each other. In particular, we argue that the size of the skyrmions will be greatly affected by the presence of the vortices offering another prospect of manipulating the skyrmionic size by the proximity to a superconductor [1]. Furthermore, we calculated the magnetic stray field and Meissner current in a superconductors S created by various nonhomogeneous magnetic texture in a F film incorporated in an S/F/S system[2] We also discuss the implications of the recent experimental results realizing these skyrmionsvortex interaction [3].
We analyse the collective modes (CM) in SFS heterostructure by taking into account the interplay between the demagnetisation field, Hdem, and the field caused by the anisotropy of the ferromagnet Han, which was previously neglected. It turns out that the spectrum of composite collective modes, ω(k), has a qualitatively different form in the case of HdemHan. In the first case, the dependence ω(k) has the same form as in previous studies, whereas in the second case, the spectrum looks completely different. In particular, for moderate or weak anisotropy in ferromagnet the group velocity of collective modes demonstrates inflection point where the group velocity become infinite and is superluminal. Furthermore, this point separates purely real and complexconjugate solutions for the collective modes and is also exception point. We show that the difference of the CMs spectra can be revealed by Fiske experiment by measuring the I−V characteristics in the presence of magnetic field and voltage[4].
[1] S. Dahir, A.F. Volkov, and I. Eremin, Interaction of Skyrmions and Pearl Vortices in SuperconductorChiral Ferromagnet Heterostructures, Phys. Rev. Lett. 122, 097001 (2019).
[2] Samme M. Dahir, Anatoly F. Volkov, and Ilya M. Eremin, Meissner currents induced by topological magnetic textures in hybrid superconductor/ferromagnet structures, Phys. Rev. B 102 , 014503 (2020)
[3] A. P. Petrović, M. Raju, X. Y. Tee, A. Louat, I. MaggioAprile, R. M. Menezes, M. J. Wyszyński, N. K. Duong, M. Reznikov, Ch. Renner, M. V. Milošević, and C. Panagopoulos, Phys. Rev. Lett. 126, 11720513 (2021).
[4] Pascal Derendorf, Anatoly F. Volkov, Ilya M. Eremin, arXiv: 2407.05457 (unpublished)

16:50  17:10

Yi Zhou
(Chinese Academy of Sciences, Beijing)
MultipleQ pair density wave in proximity to a nested Fermi surface
We show that spontaneous timereversalsymmetry (TRS) breaking can naturally arise from the interplay between pair density wave (PDW) ordering at multiple momenta and nesting of Fermi surfaces (FS). Concretely, we consider the PDW superconductivity on a hexagonal lattice with nested FS at 3/4 electron filling, which is related to a recently discovered superconductor CsV3Sb5. Because of nesting of the FS, each momentum on the FS has at least two counterparts on the FS to form finite momentum Cooper pairs, resulting in a TRS and inversion broken PDW state with stable Bogoliubov Fermi pockets. Possible implications to the Kagome superconductor CsV3Sb5 and future experiments will be discussed.

17:10  17:30

Stefan Kirchner
(National Yang Ming Chiao Tung University)
Effects of spin orbit coupling in superconducting proximity devices  application to \(CoSi_2/TiSi_2\) heterostructures
Early proposals for creating Majorana zero modes involve spin triplet superconductivity while almost all known superconductors belong to the spin singlet class with a few possible exceptions. As a result, various ingenious heterostructures of superconducting nanowires have been proposed to generate the required pwave pairing component.
In this presentation, I will review the recent findings of twocomponent superconductivity with a dominant pwave part in CoSi2/TiSi2 heterostructures In particular, I will review the effect of interfaceinduced Rashba spin orbit coupling on the conductance of a three terminal ``T" shape superconducting device and present our calculations for the differential conductance for this device within the quasiclassical formalism that includes the mixing of tripletsinglet pairing due to the Rashba spin orbit coupling.

17:30  17:50

Peter Thalmeier
(Max Planck Institute for Chemical Physics of Solids)
Order parameters and excitations in felectron compounds
The low energy crystalline electric field states and heavy electron bands
in strongly correlated 4f and 5f electron compounds exhibit possibilities
of broken symmetry states and collective excitations at low temperatures as
well as distinct interaction effects with the lattice. Characteristic
examples such as charge ordering, multipolar order and coexistence of
magnetism and unconventional superconductivity is presented, focusing on
the Ce Yb and U based compounds, including the most prominent heavy
fermmion materials. Emphasis is also placed on the methods to investigate
order parameter symmetries and the associated collective excitations.

18:00  19:30

dinner
