Date/Time: 11.19 周二16:00 (玉泉教十二 201) 19 November 2019, 16:00 (Yuquan Blg 12, Room 201)

Speaker: Ching Hua Lee (National University of Singapore, Singapore)

Title: The interesting physics of Non-Hermitian systems

Abstract: Besides gain or dissipation, open systems exhibit a variety of interesting physical effects with no Hermitian analogs. In particular, systems with asymmetric gain/loss experience the so-called non-Hermitian skin effect, where all eigenmodes localize at the boundaries, breaking down the bulk picture that forms the foundation of much of conventional topological descriptions. The resultant skin modes lead to modified topological invariants and, in higher dimensions, new families of skin-topological modes characterized by the spontaneous breaking of reciprocity. Their effective description implies an emergent non-locality that also leads to discontinuous Berry curvature, anomalous linear responses and unusual topological transitions that do not close the gap. At the many-body level, the skin effect also causes the formation of a real-space Fermi surface that renormalizes the effective temperature and produces unconventional entanglement entropy scaling. In this talk, I shall give an overview of these fascinating properties of non-Hermitian lattices, and highlight various avenues for realizing them, from cold atom proposals to recent experiments based on mechanical, optical and electrical circuit setups.

Bio: Dr. Ching Hua Lee obtained a PhD from Stanford University in 2015 under the supervision of Xiao-Liang Qi. He is current an adjunct assistant professor at the National University of Singapore, where he mainly works on novel non-equilibrium Floquet and non-Hermitian phenomena, as well as their physical realizations in various classical and quantum setups.