Spin-orbit–induced spin splittings in polar transition metal dichalcogenide monolayers

TLDR

The Rashba effect has been extensively studied in quasi two‑dimensional materials, but interest in truly two‑dimensional systems has only recently emerged after graphene’s discovery. The study uses ab initio electronic‑structure, phonon, and molecular‑dynamics calculations to investigate the structural stability and spin‑orbit–induced spin splitting in transition‑metal dichalcogenide monolayers MXY (M = Mo, W; X, Y = S, Se, Te). The authors show that increasing the spin‑orbit coupling and/or the potential gradient can enhance the Rashba splitting. They find that in polar MXY monolayers the Rashba splitting at the Γ‑point of the uppermost valence band originates from broken mirror symmetry, unlike in non‑polar systems.

Abstract

The Rashba effect in quasi two-dimensional materials, such as noble metal surfaces and semiconductor heterostructures, has been investigated extensively, while interest in real two-dimensional systems has just emerged with the discovery of graphene. We present ab initio electronic structure, phonon, and molecular-dynamics calculations to study the structural stability and spin-orbit?induced spin splitting in the transition metal dichalcogenide monolayers MXY (M?=?Mo, W and X, Y?=?S, Se, Te). In contrast to the non-polar systems with X?=?Y, in the polar systems with X ? Y the Rashba splitting at the ?-point for the uppermost valence band is caused by the broken mirror symmetry. An enhancement of the splitting can be achieved by increasing the spin-orbit coupling and/or the potential gradient.