Polarons shape the interlayer exciton emission of MoSe$_2$/WSe$_2$ heterobilayers

Abstract: We present time-resolved and CW optical spectroscopy studies of interlayer excitons (IXs) in 2$H-$ and 3$R-$stacked MoSe$_2$/WSe$_2$ heterobilayers and obtain evidence for the strong participation of hot phonons in the underlying photo-physics. Photoluminescence excitation spectroscopy reveals that excess energy associated with optical excitation of \textit{intra}-layer excitons and relaxation to IXs affects the overall IX-PL lineshape, while the spectrally narrow emission lines conventionally associated with moir\'e IXs are unaffected. A striking uniform line-spacing of the sharp emission lines is observed together with temperature and excitation level dependent spectra suggesting an entirely new picture that photo-generated phonons lead to phonon-replicas shaping the IX-emission. Excitation power and time resolved data indicate that these features are polaronic in nature. Our experimental findings modify our current understanding of the photophysics of IXs beyond current interpretations based on moir\'e-trapped IXs.