Three-Dimensional Topological States of Phonons with Tunable Pseudospin Physics
(a) Atomic structure (left) and Brillouin zone (right) of a 3D triangular lattice with two sublattices A and B. Bond lengths are denoted by lattice parameters ,, and . (b) Schematic pseudospin states of in-phase “I” (out-of-phase “O”) vibrational modes, whose pseudoangular momentum is labelled. (c) Dispersion curves of a type-I phononic TI. Blue (red) color is used to denote the contribution of I (O) vibrational modes. (d) Local density of states (LDOS) of the (001) surface, where higher (lower) LDOS are colored red (blue). (e) Schematic phonon dispersion and pseudospin textures in the plane near . The bottom panel displays pseudospin textures of O (left) and I (right) vibrational modes from the top view.