  Spins confined to point defects in atomically-thin semiconductors constitute
well-defined atomic-scale quantum systems that are being explored as single
photon emitters and spin qubits. Here, we investigate the in-gap electronic
structure of individual sulphur vacancies in molybdenum disulphide (MoS2)
monolayers using resonant tunneling scanning probe spectroscopy in the Coulomb
blockade regime. Spectroscopic mapping of defect wavefunctions reveals an
interplay of local symmetry breaking by a charge-state dependent Jahn-Teller
lattice distortion that, when combined with strong (~100 meV) spin-orbit
coupling, leads to a locking of an unpaired spin-1/2 magnetic moment to the
lattice at low temperature, susceptible to lattice strain. Our results provide
new insights into spin and electronic structure of vacancy induced in-gap
states towards their application as electrically and optically addressable
quantum systems.
