The optical response of artificially twisted MoS$_2$ bilayers

TL;DR

This study investigates how twisting layers of MoS$_2$ affects their optical properties, revealing the relationship between twist angle, interlayer coupling, and electronic state hybridization through Raman and photoluminescence analysis.

Contribution

It provides a comprehensive optical characterization of artificially twisted MoS$_2$ bilayers, highlighting how twist angle influences interlayer coupling and excitonic emissions.

Findings

Interlayer coupling strength varies with twist angle.

Interlayer exciton emission appears at specific angles.

Temperature affects emission energies and intensities.

Abstract

Two-dimensional layered materials offer the possibility to create artificial vertically stacked structures possessing an additional degree of freedom - $the$ $interlayer$ $twist$. We present a comprehensive optical study of artificially stacked bilayers (BLs) MoS$_2$ encapsulated in hexagonal BN with interlayer twist angle ranging from 0 to 60 degrees using Raman scattering and photoluminescence spectroscopies. It is found that the strength of the interlayer coupling in the studied BLs can be estimated using the energy dependence of indirect emission versus the A$_\textrm{1g}$-E$_\textrm{2g}^1$ energy separation. Due to the hybridization of electronic states in the valence band, the emission line related to the interlayer exciton is apparent in both the natural (2H) and artificial (62$^\circ$) MoS$_2$ BLs, while it is absent in the structures with other twist angles. The interlayer coupling energy is estimated to be of about 50 meV. The effect of temperature on energies and intensities of the direct and indirect emission lines in MoS$_2$ bilayers is also quantified.