Combined Theory and Scanning Tunnelling Experimental Study of Co-Filled Sulfur Vacancy in WS₂

Transition metal dichalcogenides (TMDCs) are of great interest for quantum information science (QIS). TMDC color centers have advantages for single photon emission by curtailing decoherence channels via dimensionality and natural low abundance of non-zero nuclear spin isotopes. They also offer direct probing of the defect electronic states with scanning tunneling microscopy (STM) and a unique way of benchmarking first principles defect computations. Recent experimental work has shown that STM can be used to also control defect formation in TMDCs. The experimental ability to control the filling of a sulfur vacancy with a substitutional metal is an especially exciting new development.<br/>We will report here on a combined theory and experimental study of the Co-filled sulfur vacancy in WS₂. Using beyond-DFT techniques (hybrid functionals and GW), we study what charge states are energetically favorable and their single-particle levels. We directly compare our theoretical results with experimental data obtained through atomically-precise scanning tunneling spectroscopy (STS) using an ultrastable, low temperature, and ultrahigh vacuum STM system. Our work demonstrates the importance of treating appropriately the amount of exact exchange used when performing hybrid computations on 2D systems. We finally discuss the properties of this Co-filled sulfur vacancy defect and its interest for QIS applications.