First principles study of twisted bilayer MoS2 through band unfolding

Yaohua Tan, and A. W. Ghosh, 74th Device Research Conference (2016).

Abstract

Two dimensional(2D) materials such as graphene and transition metal dichalcogenides(TMDs) are exciting candidates for electronic and optoelectronic device applications[1, 2]. In particular, there is growing interest in stacked 2D materials that often arise naturally, and also provide added possibilities for desired functionalities with varying thickness and composition. It is essential to understand the electronic properties of stacked 2D materials such as twisted multilayer TMDs and TMD het-erostructures are sensitive to inter-layer interactions [3,4]. The translational symmetry of a twisted multilayer TMD is compromised due to the twist angle. Consequently a supercell much larger than the primitive unit cell needs to be considered, creating a spaghetti-like band structure from band folding[6]. The challenge for theoretical studies of twisted multilayer systems is to extract inter-layer interactions from the folded band structures. In this work, band structures of twisted bilayer TMDs are studied using first principles calculations. In order to extract the band-edge splittings relavent to inter-layer interactions, we apply a band unfolding technique [5, 6] to the twisted bilayer TMDs. Multi-valley effective mass models are then created to model the bandedges at the Γ point as well as indirect conduction bands along K directions.