Interlayer Raman modes in twisted bilayer TMDCs

TL;DR

This paper introduces a Raman spectroscopy method to analyze interlayer coupling in twisted bilayer TMDCs, revealing how the C-exciton resonance enhances interlayer Raman modes, which serve as a measure of interlayer interaction.

Contribution

It demonstrates that optical interlayer Raman modes, activated at the C-exciton resonance, can quantify interlayer coupling in twisted bilayer TMDCs, advancing understanding of their physical properties.

Findings

Interlayer Raman modes are enhanced at the C-exciton resonance.

These modes can be used to measure interlayer coupling strength.

The approach provides insights into the electronic interactions in twisted bilayer TMDCs.

Abstract

Twisted bilayer two-dimensional transition-metal dichalgocenides (TMDCs) exhibit a range of novel phenomena such as the formation of moir\'e excitons and strongly correlated phases. The coupling between the layers is crucial for the resulting physical properties and depends not just on the twist angle but also on the details of the fabrication process. Here, we present an approach for the analysis of this interlayer coupling via Raman spectroscopy. By exciting the C-exciton resonance of the TMDCs, optical (high-frequency) interlayer Raman modes are activated that are too weak in intensity at excitation energies far below the C exciton. This is due to the wave function of the C exciton, which expands - in contrast to A and B excitons - over both layers and, therefore, couples the layers electronically. We present optical interlayer Raman modes in twisted 2L TMDCs and show that they can be used as a measure of the interlayer coupling between the individual layers.