A Tight Binding Approach to Strain and Curvature in Monolayer Transition-Metal Dichalcogenides

TL;DR

This paper develops a tight binding model for monolayer transition-metal dichalcogenides that incorporates strain and curvature effects, enabling precise tuning of electronic properties through mechanical deformations.

Contribution

It introduces a comprehensive low-energy Hamiltonian that accounts for both strain and curvature effects on electronic structure in monolayer transition-metal dichalcogenides.

Findings

Local lattice area variations tune band gap and effective masses.

Uniaxial strain reduces the direct band gap at the K point.

Curvature induces an effective magnetic field and Rashba-like spin-orbit coupling.

Abstract

We present a model of the electronic properties of monolayer transition-metal dichalcogenides based on a tight binding approach which includes the effects of strain and curvature of the crystal lattice. Mechanical deformations of the lattice offer a powerful route for tuning the electronic structure of the transition-metal dichalcogenides, as changes to bond lengths lead directly to corrections in the electronic Hamiltonian while curvature of the crystal lattice mixes the orbital structure of the electronic Bloch bands. We first present an effective low energy Hamiltonian describing the electronic properties near the K point in the Brillouin zone, then present the corrections to this Hamiltonian due to arbitrary mechanical deformations and curvature in a way which treats both effects on an equal footing. This analysis finds that local area variations of the lattice allow for tuning of the band gap and effective masses, while the application of uniaxial strain decreases the magnitude of the direct band gap at the K point. Additionally, strain induced bond length modifications create a fictitious gauge field with a coupling strength that is smaller than that seen in related materials like graphene. We also find that curvature of the lattice leads to the appearance of both an effective in-plane magnetic field which couples to spin degrees of freedom and a Rashba-like spin-orbit coupling due to broken mirror inversion symmetry.