Chiral phonon in the cubic system based on the Laves phase of [formula omitted]Bi2 ([formula omitted] K, Rb, Cs)

Abstract

AB2 (A= K, Rb, Cs) compounds crystallize in the cubic Laves phase (symmetry Fd3̄m). The geometry of the crystal structure allows the realization of chiral phonons, which are associated with the circulation of atoms around their equilibrium positions. Due to the inversion symmetry and time reversal symmetry, total pseudo-angular momentum (PAM) of the system vanishes. We show that the doping of these system can lead to a new phase with symmetry F4̄3m. New systems (KRbBi4 and RbCsBi4) do not exhibit soft modes (are stable dynamically). Due to the inversion symmetry breaking, realized chiral phonon modes possess a non-zero total PAM. In both type of systems the chiral phonons are realized for the wavevectors at the edge of the Brillouin zone. This study explores the possibility of chiral phonon engineering via doping, and predicts two new materials. Discussing the problem opens a new way to study the phonon Hall effect.