Raman-scattering study of the phonon dispersion in twisted bi-layer graphene

TL;DR

This study demonstrates how superlattice-induced Raman scattering in twisted bi-layer graphene can be used to probe its phonon dispersion, revealing layer breathing vibrations despite the lack of stacking order.

Contribution

It introduces a novel Raman scattering method to analyze phonon dispersion in twisted bi-layer graphene using superlattice effects.

Findings

Superlattice-induced Raman scattering probes phonon dispersion.

Layer breathing vibrations are observed in tBLG.

The effect differs from double-resonance phenomena.

Abstract

Bi-layer graphene with a twist angle \theta\ between the layers generates a superlattice structure known as Moir\'{e} pattern. This superlattice provides a \theta-dependent q wavevector that activates phonons in the interior of the Brillouin zone. Here we show that this superlattice-induced Raman scattering can be used to probe the phonon dispersion in twisted bi-layer graphene (tBLG). The effect reported here is different from the broadly studied double-resonance in graphene-related materials in many aspects, and despite the absence of stacking order in tBLG, layer breathing vibrations (namely ZO' phonons) are observed.