Phononic topological insulators with tunable pseudospin physics

TL;DR

This paper introduces tunable pseudospins as a new way to control phonons, revealing topological insulators with protected surface states that enable unconventional phonon transport for advanced phononic devices.

Contribution

It proposes using crystalline symmetry-protected pseudospins for phonon manipulation and reports two types of three-dimensional phononic topological insulators with novel surface states.

Findings

Discovery of pseudospin-momentum locking in phononic surface states

Identification of two types of 3D phononic topological insulators

Potential applications in phononic circuits and devices

Abstract

Efficient control of phonons is crucial to energy-information technology, but limited by the lacking of tunable degrees of freedom like charge or spin. Here we suggest to utilize crystalline symmetry-protected pseudospins as new quantum degrees of freedom to manipulate phonons. Remarkably, we reveal a duality between phonon pseudospins and electron spins by presenting Kramers-like degeneracy and pseudospin counterparts of spin-orbit coupling, which lays the foundation for "pseudospin phononics". Furthermore, we report two types of three-dimensional phononic topological insulators, which give topologically protected, gapless surface states with linear and quadratic band degeneracies, respectively. These topological surface states display unconventional phonon transport behaviors attributed to the unique pseudospin-momentum locking, which are useful for phononic circuits, transistors, antennas, etc. The emerging pseudospin physics offers new opportunities to develop future phononics.