Stacking-dependent shear modes in trilayer graphene

TL;DR

This study reveals that the Raman spectra of shear modes in trilayer graphene are highly dependent on stacking order, with ABA and ABC configurations showing distinct responses due to their symmetry differences.

Contribution

The paper demonstrates the stacking-dependent Raman shear mode behavior in trilayer graphene, highlighting a unique characteristic not observed in layer-breathing modes.

Findings

ABA trilayers show strong high-frequency shear mode response.

ABC trilayers show strong low-frequency shear mode response.

Shear mode behavior is linked to symmetry differences.

Abstract

We observed distinct interlayer shear mode Raman spectra for trilayer graphene with ABA and ABC stacking order. There are two rigid-plane shear-mode phonon branches in trilayer graphene. We found that ABA trilayers exhibit pronounced Raman response from the high-frequency shear branch, without any noticeable response from the low-frequency branch. In contrast, ABC trilayers exhibit no response from the high-frequency shear branch, but significant Raman response from the low-frequency branch. Such complementary behaviors of Raman shear modes can be explained by the distinct symmetry of the two trilayer allotropes. The strong stacking-order dependence was not found in the layer-breathing modes, and thus represents a unique characteristic of the shear modes.