Moiré-enabled spin pumping and preservation in MoSe₂/WS₂ heterobilayers

Charge carriers can exhibit new quantum phases with charge ordering in transition metal dichalcogenide (TMDC) heterostructures supporting moiré superlattices. To date, however, the influence of the moiré potential on the spin properties of the carriers has been much less studied. Here, we have examined how spin relaxation is influenced by the presence of a moiré superlattice.

To probe spin relaxation rates, we first created a spin-valley population difference in an electron doped MoSe₂/WS₂ heterobilayer by pumping with circularly polarized light. We subsequently measured the relaxation rate by following the time evolution of the circular dichroism induced by the spin polarization. The photogenerated excitons, we note, relax on a much faster time scale. At temperatures of a few Kelvin where zone-edge phonons are frozen out, we observed spin relaxation lifetimes approaching one millisecond. This measured (longitudinal) relaxation time exceeds by two or more orders of magnitude that found in the corresponding monolayer systems, setting a record for mobile electrons in solids.  We will discuss why the spin relaxation process is expected to become substantially less effective in the moiré heterobilayer based on a conventional k⋅p approach combined with density-functional theory.