Optically and Electrically Controllable Adatom Spin–orbital Dynamics in Transition Metal Dichalcogenides*

We analyze the interplay of spin-valley coupling, orbital physics, and magnetic anisotropy taking place at single magnetic atoms adsorbed on semiconducting transition metal dichalcogenides, MX₂ (M = Mo, W; X = S, Se). Orbital selection rules turn out to govern the kinetic exchange coupling between the adatom and charge carriers in the MX₂ and lead to highly orbitally dependent spin-flip scattering rates, as we illustrate for the example of transition metal adatoms with d⁹ configuration. Our ab initio calculations suggest that d⁹ configurations are realizable by single Co, Rh, or Ir adatoms on MoS₂, which additionally exhibit a sizable magnetic anisotropy. We find that the interaction of the adatom with carriers in the MX₂ allows to tune its behavior from a quantum regime with full Kondo screening to a regime of ”Ising spintronics” where its spin–orbital moment acts as classical bit, which can be erased and written electronically and optically.