Three-Dimensional Topological States of Phonons with Tunable Pseudospin Physics
(a) Schematic phonon tunneling junction, where surface lattice vibrations of frequency are excited (detected) by a point-like source (probe) and a tunneling barrier is applied by a piezoelectric gate. Schematic phonon dispersion and pseudospin textures of type-I (type-II) TSSs are displayed in the top (bottom) panel. (b) Phonon transmission as a function of incident angle for type-I TSSs (red dash-dotted), type-II TSSs (purple solid), and normal surface states (black dashed), for which we used barrier widths of , , and , respectively. is the length parameter depicted in Figure 1(a). is defined along the -axis. (c) Phonon transmission as a function of for . and were used.