Mass inversion in graphene by proximity to dichalcogenide monolayer

TL;DR

This paper investigates how proximity effects in graphene on TMD substrates induce spin-orbit coupling and phase transitions, revealing potential for quantum spin Hall and valley Hall effects in experimentally accessible systems.

Contribution

It introduces an effective Hamiltonian capturing symmetry breaking in graphene due to TMD substrates, predicting an inverted mass gap regime and phase transitions validated by tight-binding calculations.

Findings

Inverted mass band gap regime identified in graphene-TMD heterostructures.

Phase transition from inverted mass to staggered gap driven by gate voltage.

Potential realization of quantum spin Hall and valley Hall effects.

Abstract

Proximity effects resulting from depositing a graphene layer on a TMD substrate layer change the dynamics of the electronic states in graphene, inducing spin orbit coupling (SOC) and staggered potential effects. An effective Hamiltonian that describes different symmetry breaking terms in graphene, while preserving time reversal invariance, shows that an inverted mass band gap regime is possible. The competition of different perturbation terms causes a transition from an inverted mass phase to a staggered gap in the bilayer heterostructure, as seen in its phase diagram. A tight-binding calculation of the bilayer validates the effective model parameters. A relative gate voltage between the layers may produce such phase transition in experimentally accessible systems. The phases are characterized in terms of Berry curvature and valley Chern numbers, demonstrating that the system may exhibit quantum spin Hall and valley Hall effects.