Circular emission under linear excitation from interlayer excitons in WSe₂/MoSe₂ heterobilayer

We report circularly polarized emission from interlayer excitons in WSe₂/MoSe₂ heterobilayer under linear excitation at zero magnetic field. The magnitude and sign of the degree of circular polarization (DCP) varies spatially over the sample. The DCP is independent of excitation energy when incident laser is linearly polarized, however, can be modulated by circular pumping or magnetic field. This is in stark contrast with WSe₂ and MoSe₂ intralayer excitons where circular emission only occurs with an applied magnetic field or under circular pumping. The observation of circularly polarized emission, in absence of magnetic field and circular pumping, implies an effective time-reversal symmetry (TRS) breaking in the WSe₂/MoSe₂ heterobilayer. As different cool downs result in very similar spatial patterns of DCP, we rule out spontaneous TRS breaking in the sample. Due to the momentum space-indirect nature of interlayer excitons, there is a finite center-of mass momentum in the recombining exciton state. This, together with the ubiquitous inhomogeneous strain in exfoliated samples can explain our observations.