Spin, orbital, and valley structure of chalcogen vacancies in monolayer MoS₂

Vacancies in 2D materials have attracted much attention recently as single photon emitters and potential spin qubits. However, an atomic-level understanding of their bound states and wave functions remains elusive. In this work, we combine low-temperature scanning tunneling microscopy (STM) and ab-initio density functional theory (DFT) calculations to unambiguously identify and characterize the single and double chalcogen vacancies in monolayer MoS₂. The real space STM images of the electronic energy levels introduced by chalcogen vacancies are explored, showing lobe-like shapes, corresponding to the unpaired electrons bound to the defects. The spin quantization axis and spin-orbit coupling are found to play key roles in the determination of direction and shape of the lobes observed in the STM images. Additionally, STM images in reciprocal space, dI/dV analysis, and density of states (DOS) are comprehensively investigated, providing a detailed understanding of the MoS₂ electronic device properties. This atomic-level analysis can also be extended to other transition-metal dichalcogenides (TMDs), which will offer useful insights for quantum computing and sensing applications.