**报告摘要：**Non-Hermitian Hamiltonian is a widely useful language in a number of branches of physics. Intriguingly, non-Hermitian systems exhibit a unique bulk-boundary correspondence beyond the conventional framework of Bloch band theory. A revised band theory based on the 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. The consequences of non-Bloch band theory are not limited to non-Hermitian topology. We show that this theory has a natural application to nonreciprocal 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 nonreciprocal amplifiers are obtained from the non-Bloch band theory.

References:

[1] S. Yao, Z. Wang, Phys. Rev. Lett. 121, 086803 (2018);

[2] S. Yao, F. Song, Z. Wang, Phys. Rev. Lett. 121, 136802 (2018);

[3] F. Song, S. Yao, Z. Wang, Phys. Rev. Lett. 123, 170401 (2019);

[4] Lei Xiao, et al. Nat. Phys. 16, 761 (2020);

[5] W.-T. Xue, M.-R. Li, Y.-M. Hu, F. Song, Z. Wang, arXiv:2004.09529

**报告人简介：**Zhong Wang finished his undergraduate education (2001-2005) and then got the doctorate (2011) from University of Science and Technology of China. During 2009-2010 he was a visiting student in Stanford University. He joined Institute for Advanced Study of Tsinghua Univeristy in 2011 as an associate member; he is now a member there. His current research interests include topological phases and topological phenomena in condensed matters, non-Hermitian physics, classical and quantum open systems, and strongly correlated systems.