The Interlayer Shear Modes in Twisted Multi-layer Graphenes: Interlayer coupling, Davydov Splitting and Intensity Resonance

TL;DR

This study uses Raman spectroscopy to investigate interlayer shear modes in twisted multilayer graphene, revealing weak coupling effects, Davydov splitting, and resonance phenomena that deepen understanding of 2D heterostructure interfaces.

Contribution

It provides the first detailed analysis of interlayer shear modes in twisted multilayer graphene, highlighting weak coupling and resonance effects not previously characterized.

Findings

Interlayer coupling at the interface is only 20% of Bernal-stacked layers.

Davydov splitting observed in shear mode frequencies.

Shear modes exhibit intensity enhancement due to optical resonance.

Abstract

Graphene and other two-dimensional crystals can be combined to form various hybrids and heterostructures, creating materials on demand, in which the interlayer coupling at the interface leads to modified physical properties as compared to their constituents. Here, by measuring Raman spectra of shear modes, we probe the coupling at the interface between two artificially-stacked few-layer graphenes rotated with respect to each other. The strength of interlayer coupling between the two interface layers is found to be only 20% of that between Bernal-stacked layers. Nevertheless, this weak coupling manifests itself in a Davydov splitting of the shear mode frequencies in systems consisting of two equivalent graphene multilayers, and in the intensity enhancement of shear modes due to the optical resonance with several optically allowed electronic transitions between conduction and valence bands in the band structures. This study paves way for fundamental understanding into the interface coupling of two-dimensional hybrids and heterostructures.