内容：

Topological states of matter provide a fertile ground for discovering new quasiparticles in condensed matter physics, such as Weyl and Dirac fermions, which were originally predicted in high-energy physics and recently observed in solid-state materials. In topological semimetals, Weyl and Dirac points correspond to two- and fourfold degenerate linear band crossing points, hallmarks of relativistic particles with half-integer spins. Remarkably, the recent discovery of triply degenerate points (TDPs) in semimetals has opened an avenue for exploring new types of quasiparticles that have no analog in quantum field theory. Such TDPs possess effective integer spins while preserving Fermi statistics and linear dispersions. In previous studies, the emergence of such protected nodes was often attributed to spin-vector-momentum couplings. In this talk, I will discuss three new types of TDPs that are classified by different monopole charges (C = +/- 2, 1, 0) and induced by the interplay between spin-tensor- and spin-vector-momentum couplings. I will discuss how to realize these new types of TDPs using ultracold atoms in optical lattices and photons in non-Hermitian hyperbolic metamaterials.  These proposed atomic and photonic systems may provide highly controllable platforms for exploring and engineering novel quasiparticles without counterparts in quantum field theory.

Relevant publications: 

[1] X.-W. Luo, K. Sun, C. Zhang, Spin-tensor--momentum-coupled Bose-Einstein condensates, Phys. Rev. Lett. 119, 193001 (2017). 

[2] H. Hu, J. Hou, F. Zhang, C. Zhang, Topological Triply-Degenerate Points Induced by Spin-Tensor-Momentum Couplings, Phys. Rev. Lett.  120, 240401 (2018).

[3] H. Hu, C. Zhang, Spin-1 Topological Monopoles in Parameter Space of Ultracold Atoms, Phys. Rev. A 98, 013627 (2018).

[4] J. Hou, Z. Li, X.-W. Luo, Q. Gu, C. Zhang, Topological bands and triply-degenerate points in non-Hermitian hyperbolic metamaterials, arXiv:1808.06972

[6] J. Hou, Z. Li, Q. Gu, C. Zhang, Non-Hermitian Photonics based on Charge-Parity Symmetry, arXiv:1904.05260

人物介绍：

Prof. Zhang received his PhD at University of Texas at Austin in 2005 and worked as a postdoctoral research associate from 2006 to 2008 at the University of Maryland at College Park. After that, he joined Washington State University at Pullman as an assistant professor. In 2012, he moved to the University of Texas at Dallas as a tenured associate professor. Currently, he is the full professor at University of Texas at Dallas. Prof. Zhang’s research interests are in theoretical atomic physics and condensed matter physics. His research activities include ultra-cold atomic gases, physical implementation of quantum information, topological superconductors, quantum chaos, physics of strongly-correlated multiferroic materials, high temperature cuprate superconductivity, and graphene. His research profile can be found at https://scholar.google.com/citations?user=dNqXfv8AAAAJ&hl=zh-CN.