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

Structural defects in 2D materials offer an effective way to engineer new material functionalities beyond conventional doping. We report on 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 and scanning tunneling microscopy. Sulfur vacancies, which are absent in as-grown samples, were deliberately created by annealing in vacuum. Two energetically narrow unoccupied defect states followed by vibronic sidebands provide a unique fingerprint of this defect. Direct imaging of the defect orbitals, together with ab initio GW calculations, reveal that the large splitting of 252±4 meV between these defect states is induced by spin-orbit coupling.We thank Andreas Schmid, Katherine Cochrane, and Nicholas Borys for constructive discussions. B. S. appreciates the support from the Swiss National Science Foundation under Project No. P2SKP2_171770. Theoretical work was supported by the Center for Computational Study of Excited State Phenomena in Energy Materials, which is funded by the U.S. Department of Energy, Office of Science, Basic Energy Sciences, Materials Sciences and Engineering Division, under Contract No. DE-AC02-05CH11231, as part of the Computational Materials Sciences Program. The materials synthesis and STM/AFM characterization was performed at the Molecular Foundry that is supported by the Office of Science, Office of Basic Energy Sciences, of the U.S. Department of Energy under the same contract number. A.W.-B. and B.S. acknowledges DOE Early Career funds to perform the work. S. R.-A. acknowledges the support of Rothschild and Fulbright fellowships. S. B. acknowledges the support of the European Union under Grant No. FP7-PEOPLE-2012-IOF-327581 and of Spanish MINECO (Grant No. MAT2017-88377-C2-1-R). This research used resources of the National Energy Research Scientific Computing Center (NERSC), a DOE Office of Science User Facility supported by the Office of Science of the U.S. Department of Energy under Contract No. DE-AC02- 05CH11231