Chiral Phonons in Moiré Superlattices

Nishchay Suri, Chong Wang, Yinhan Zhang, Di Xiao

Published 2021-08-30Version 1

We theoretically demonstrate that moir\'e phonons at the lowest-energy bands can become chiral. A general symmetry analysis reveals that they originate from stacking configurations leading to an asymmetric interlayer binding energy that breaks the $C_{2z}$ symmetry on the moir\'e length scale. Within elastic theory, we provide a complete classification of van der Waals heterostructures in respect to hosting moir\'e chiral phonons and discuss their emergence in twisted bilayer MoS$_2$ as an example. The formation of the chiral phonons can be qualitatively understood using an effective model, which emphasizes their origin in the energy difference between stacking domains. Since moir\'e chiral phonons are highly tunable, with excitation energies in only a few meV, and moir\'e scale wavelengths, they might find potential applications in phononic twistronic devices.