Effect of spin-dependent tunneling in a MoSe${}_2$/Cr${}_2$Ge${}_2$Te${}_6$ van der Waals heterostructure on exciton and trion emission

We study van der Waals heterostructures consisting of monolayer MoSe${}_2$ and few-layer Cr${}_2$Ge${}_2$Te${}_6$ fully encapsulated in hexagonal Boron Nitride using low-temperature photoluminescence and polar magneto-optic Kerr effect measurements. Photoluminescence characterization reveals a partial quenching and a change of the exciton-trion emission ratio in the heterostructure as compared to the isolated MoSe${}_2$ monolayer. Under circularly polarized excitation, we find that the exciton-trion emission ratio depends on the relative orientation of excitation helicity and Cr${}_2$Ge${}_2$Te${}_6$ magnetization, even though the photoluminescence emission itself is unpolarized. This observation hints at an ultrafast, spin-dependent interlayer charge transfer that competes with exciton and trion formation and recombination.