Abstract
Topological materials exhibit novel properties, e.g., symmetry protected surface states, quantized conductivity, etc. In this talk, various topological phases in realistic materials will be reported, including the topology in electronic band structures and phonon spectra. The four-fold Dirac points are firstly identified that are stable against spin-orbit coupling in two-dimensional (2D) system without inversion symmetry. Such topological phase has nonzero Berry curvature near the Dirac nodes, and two edge states connect one pair of the Dirac points. The 2D SbSSn is then predicted to host such Dirac points, thus facilitates their experimental observations. For topological phonon spectra, carbon allotropic phase bcc-C8 is identified to host three intersecting nodal ring phonons perpendicular to each other. The intersecting phonon nodal rings with quantized Berry phase π are protected by parity-time symmetry, guaranteeing the drumhead surface states on semi-infinite (001) and (110) surfaces. Besides, it is verified that the three-dimensional (3D) irreducible representations (IRs) of chiral point groups, O(432) and T(23), will host spin-1 Weyl phonons. The spin-1 Weyl phonons inevitably split into quadratic Weyl phonons if 3D IRs are decomposed into 2D IRs. This latter finding builds the connection between different double Weyl phonons and provides guidance for investigating the splitting behavior among other high Chern number quasiparticles. All these results demonstrate that the interplay between symmetry and topology can help us to understand the properties of band topology.
Anyone interested is welcome to attend.