Large spin-orbit splitting of deep in-gap defect states of engineered sulfur vacancies in monolayer WS2

TL;DR

This study combines advanced microscopy and theoretical calculations to reveal that sulfur vacancies in monolayer WS2 exhibit a large spin-orbit splitting of 252 meV in their defect states, enabling tailored material functionalities.

Contribution

It provides the first direct experimental and theoretical evidence of large spin-orbit splitting in sulfur vacancy defect states of WS2, linking atomic structure to electronic properties.

Findings

Sulfur vacancies create two narrow unoccupied defect states.

The defect states show a large 252 meV spin-orbit splitting.

Controlled vacancy creation offers new material engineering possibilities.

Abstract

Structural defects in 2D materials offer an effective way to engineer new material functionalities beyond conventional doping in semiconductors. Specifically, deep in-gap defect states of chalcogen vacancies have been associated with intriguing phenomena in monolayer transition metal dichalcogenides (TMDs). Here, we report the direct experimental correlation of the atomic and electronic structure of a sulfur vacancy in monolayer WS2 by a combination of CO-tip noncontact atomic force microscopy (nc-AFM) and scanning tunneling microscopy (STM). Sulfur vacancies, which are absent in as-grown samples, were deliberately created by annealing in vacuum. Two energetically narrow unoccupied defect states of the vacancy provide a unique fingerprint of this defect. Direct imaging of the defect orbitals by STM and state-of-the-art GW calculations reveal that the large splitting of 252 meV between these defect states is induced by spin-orbit coupling. The controllable incorporation and potential decoration of chalcogen vacancies provide a new route to tailor the optical, catalytic and magnetic properties of TMDs.