Exciton-Exciton Interactions Revealed through Interlayer Photoresponse of a Graphene-MoTe₂-Graphene Heterostructure Photocell

Heterostructures composed of atomic layer materials bonded through van-der-Waals interactions have demonstrated great potential for use in next generation optoelectronic devices. However, the role of strong exciton-exciton interactions in the interlayer photocurrent in such devices is not fully understood. Utilizing a newly developed dynamic photoresponse microscopy technique, we gain a comprehensive understanding of the MoTe₂ heterostructure photoresponse. The power dependence of the interlayer photocurrent is well described by a single power law, where the power law exponent parameterizes the non-linearity of the photoresponse. We develop a detailed model that accounts for careful time integration of the dynamics, resulting in an analytic solution that reproduces the non-linear power dependence. We attribute the strong sub-linear power dependence to electron-hole generation and exciton-exciton annihilation. Additionally, we spatially resolve the deviations from this conventional power law behavior, which suggest a breakdown of the exciton-exciton annihilation model and the emergence of a novel electronic phase.