Topic: Non-Hermitian topological states and non-Bloch band theory

Speaker: Prof. Zhong Wang

Coordinates: PCFT C1124, 4pm, Thursday, Jul. 1

Abstract: Non-Hermitian Hamiltonian is a widely useful language in a number of branches of physics. Recently, it has been found that non-Hermitian systems exhibit a unique bulk-boundary correspondence beyond the conventional framework of Bloch band theory. A revised band theory based on the concept of generalized Brillouin zone, now known as the non-Bloch band theory, has been formulated to understand the non-Hermitian topology.  To predict the topological edge modes, topological invariants are defined in the generalized Brillouin zone rather than in the standard Brillouin zone. We show that the non-Bloch band theory also has natural applications beyond topology. As an example, we study directional amplification, a phenomenon that waves are amplified in a preferred propagation direction while suppressed in the reversed direction. Compact formulas for the gain and directionality of directional amplifiers are obtained from the new band theory.