Oral Session B3 (Wednesday, February 14)
Chair: Maria A. H. Vozmediano,
Instituto de Ciencia de Materiales de Madrid (ICMM - CSIC)

Special Session Talk
14: 00 - 14 : 40

Shinsei Ryu
Department of Physics, Princeton University

Topological phenomena out of equilibrium
and time-reversal symmetry
Time reversal symmetry plays a crucial role in topological phenomena in many-body quantum
physics. One of the prime examples include topological insulators that have been studied
extensively in modern condensed matter physics. Recent investigations have expanded the scope toinclude non-equilibrium settings, such as driven (Floquet) systems, and topological phenomena inopen quantum systems. In this talk, I will discuss the implication of time-reversal symmetry in
out-of-equilibrium quantum many-body systems. In particular, we discuss the so-called
Kubo-Martin-Schwinger (KMS) symmetry, and the role it plays in drive/open quantum
many-body systems. Specifically, we discuss topological phenomena protected by the KMS
symmetry and quantum anomalies associated to the KMS symmetry with applications to theLieb-Schultz-Mattis type theorem.
References[1] Yuhan Liu, Hassan Shapourian, Paolo Glorioso, and Shinsei Ryu, “Gauging anomalous unitaryoperators”, Phys. Rev. B 104, 155144 (2021).
[2] Kohei Kawabata, Anish Kulkarni, Jiachen Li, Tokiro Numasawa, and Shinsei Ryu, “Symmetry of Open
Quantum Systems: Classification of Dissipative Quantum Chaos”, PRX Quantum 4, 030328 (2023)[3] Kohei Kawabata, Ramanjit Sohal and Shinsei Ryu, “Lieb-Schultz-Mattis Theorem in Open QuantumSystems”, arXiv:2305.16496

Oral Session B3 (Wednesday, February 14)
Chair: Maria A. H. Vozmediano,
Instituto de Ciencia de Materiales de Madrid (ICMM - CSIC)

Special Session Talk
14: 40 - 15 : 20

Takashi Oka
The Institute for Solid State Physics (ISSP), The University of Tokyo

Heterodyne Hall eﬀect in oscillating
magnetic fields
Floquet engineering [1] introduces new dynamical functions within quantum materials. The
process of heterodyning, a signal processing technique, produces output signals by combining an
input signal with the dynamics of a designated multiplier [2]. This multiplier operates as a Floquet
system, which is periodically influenced by an external drive over time [2, 3]. By designating
electrons in oscillating magnetic fields as this multiplier, the Heterodyne Hall eﬀect can beachieved [2]. We have recently broadened this concept to encompass 2D Dirac electrons, leading
to the discovery of Floquet Landau levels and an eﬀect reminiscent of the chiral magnetic eﬀect[4].
References[1] T. Oka and S. Kitamura, Annu. Rev. Condens. Matter Phys. 10, 387 (2019).
[2] T. Oka, L. Bucciantini, Phys. Rev. B 94, 155133 (2016).
[3] A. Kumer, M. Rodriguez-Vega, T. Pereg-Barnea, B. Seradjeh, Phys. Rev. B 101, 174314 (2020).
[4] S. Kitamura, T. Oka, in preparation.

Oral Session B3 (Wednesday, February 14)
Chair: Maria A. H. Vozmediano,
Instituto de Ciencia de Materiales de Madrid (ICMM - CSIC)

Contributed Oral
15: 20 - 15 : 40

Nonlinear optical responses in ɑ-type organic salt
Keisuke Kitayama1 and Masao Ogata1, 2
1. Department of Physics, University of Tokyo, Hongo, Bunkyo-ku, Tokyo 113-0033, Japan
2. Trans-scale Quantum Science Institute, University of Tokyo, Bunkyo-ku, Tokyo 113-0033, Japan
Nonlinear optical responses, such as shift current, have been extensively explored from the perspectives of both
fundamental science and electronic applications. However, nonperturbative eﬀects in multiband systems are notwell understood.
In this talk, we investigate the shift current induced by linearly polarized light in ɑ-(BEDT-TTF)2I3 [see Fig. (a)][1]. In our previous studies, we have theoretically predicted various photoinduced topological phase transitions inthis material [2-5]. By applying the perturbation theory, we determine the dependencies of the shift current on thefrequency of light. Notably, we discover that the direction of the shift current strongly depends on the frequency oflight, and this unique dependence is attributed to multiband eﬀects. Furthermore, we explore the nonperturbativeeﬀects of the shift current using the Floquet Hamiltonian [see Fig. (b)]. Our findings reveal a sign change in thisresponse, a phenomenon not observable when considering only the second-order response. We discuss thelimitations of both the equation derived by the perturbation theory and the one derived by Morimoto andNagaosa [6] when the light intensity is large.
References[1] K. Kitayama and M. Ogata, arXiv:2311.07176 (2023).
[2] K. Kitayama and M. Mochizuki, Phys. Rev. Research 2, 023229 (2020).
[3] K. Kitayama, M. Mochizuki, Y. Tanaka, and M. Ogata, Phys. Rev. B 104, 075127 (2021).
[4] K. Kitayama, Y. Tanaka, M. Ogata, and M. Mochizuki, J. Phys. Soc. Jpn. 90, 104705 (2021).
[5] K. Kitayama, M. Ogata, M. Mochizuki, and Y. Tanaka, J. Phys. Soc. Jpn. 91, 104704 (2021).
[6] T. Morimoto and N. Nagaosa, Science Advances 2, e1501524 (2016).