The spin-orbit coupling (SOC) effect has been known to be profound in monolayer pristine transition metal dichalcogenides (TMDs). Here we show that point defects, which are omnipresent in the TMD membranes, exhibit even stronger SOC effects and change the physics of the host materials drastically. In this article we chose the representative monolayer ${\mathrm{WS}}_2$ slabs from the TMD family together with seven typical types of point defects including monovacancies, interstitials, and antisites. We calculated the formation energies of these defects, and studied the effect of spin-orbit coupling (SOC) on the corresponding defect states. We found that the S monovacancy (${\mathrm{V}}_{\mathrm{S}}$) and S interstitial (adatom) have the lowest formation energies. In the case of ${\mathrm{V}}_{\mathrm{S}}$ and both of the ${\mathrm{W}}_{\mathrm{S}}$ and ${\mathrm{W}}_{\mathrm{S}2}$ antisites, the defect states exhibit strong splitting up to 296 meV when SOC is considered. Depending on the relative position of the defect state with respect to the conduction band minimum (CBM), the hybrid functional HSE will either increase the splitting by up to 60 meV (far from CBM), or decrease the splitting by up to 57 meV (close to CBM). Furthermore, we found that both the ${\mathrm{W}}_{\mathrm{S}}$ and ${\mathrm{W}}_{\mathrm{S}2}$ antisites possess a magnetic moment of 2 ${\mu }_B$ localized at the antisite W atom and the neighboring W atoms. The dependence of SOC on the orientation of the magnetic moment for the ${\mathrm{W}}_{\mathrm{S}}$ and ${\mathrm{W}}_{\mathrm{S}2}$ antisites is discussed. All these findings provide insights in the defect behavior under SOC and point to possibilities for spintronics applications for TMDs.

• Received 9 June 2016
• Revised 29 August 2016

DOI:https://doi.org/10.1103/PhysRevB.94.195425