Chiral Phonons in Moiré Superlattices

Abstract

We discover chiral phonons at the lowest-energy bands in moiré superlattices. The moiré chiral phonons we uncover are the collective excitations of the stacking domains. Their origin is uniquely attributed to the stacking configurations whose interlayer binding energy breaks the $C_{2z}$ symmetry on the moiré length scale. Within elastic theory, we use a general symmetry analysis to provide a complete classification of van der Waals heterostructures in respect to hosting moiré chiral phonons and show the calculation for twisted MoS${}_2$ as an example. We present a low-energy effective model to qualitatively understand the moiré chiral phonons and show that it captures the essential physics remarkably well. Our result potentially opens up new possibilities in phononic twistronics as the moiré chiral phonons have high tunability, moiré scale wavelengths, excitation energies in only a few meV, and can possibly be mechanically excited.

5 pages and 5 figures of main text + 5 pages and 1 figure of supplementary

References in corpus (3)

• Moiré heterostructures as a condensed matter quantum simulator
• Valley Phonons and Exciton Complexes in a Monolayer Semiconductor
• Multipath optical recombination of intervalley dark excitons and trions in monolayer WSe${}_2$

Cited by in corpus (8)

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• Moiré phonons and impact of electronic symmetry breaking in twisted trilayer graphene
• Moiré phonons in graphene/hexagonal boron nitride moiré superlattice
• Chiral phonons in binary compounds $A$Bi ($A$ = K, Rb, Cs) with P2${}_1$/c structure
• Physics of Phonons in Systems with Approximate Screw Symmetry
• Group Theory Analysis of Phonons in Monolayer Chromium Trihalides and Their Janus Structures
• Chiral phonon in the cubic system based on the Laves phase of $A$Bi${}_2$ ($A=$K, Rb, Cs)