Saitama University

Abstract:

Nonlinear response has become a powerful probe of condensed-matter systems because it encodes inversion-symmetry breaking, higher-order geometry, and dissipation, and it may enable high-frequency rectification. While experiments increasingly point to crucial roles of dissipation and strong correlations in generating large nonlinear signals, these aspects remain insufficiently understood.

In this talk, I present a diagrammatic framework for nonlinear responses in strongly correlated electron systems that explicitly incorporates mass renormalization and the structure of dissipation, the latter captured as a non-Hermitian effect. We show that a quasiparticle renormalization factor γ(>1) amplifies the nnn-th-order response by γ^(n−1). Moreover, non-orthogonality inherent to the non-Hermitian sector naturally leads to an extension of quasiparticle lifetimes.

If time allows, I will also briefly discuss recent work applying reinforcement learning to accelerate exploration and optimization in correlated-electron models.

Bio:

Yoshihiro Michishita (道下佳寛) received his Ph.D. in physics from Kyoto University, where his doctoral thesis focused on non-Hermitian aspects of strongly correlated electron systems. He went on to work as a postdoctoral researcher at the RIKEN Center for Emergent Matter Science, and later as a research scientist in industry. Since 2025 he has been a researcher in the Shinaoka Laboratory at Saitama University, where he will take up a faculty position as Assistant Professor in October 2025. His research interests span condensed matter theory and machine learning techniques.

Contact: Lei Wang (9853)

Location:M830