Strong evidence of inter-layer optical phonons and low-temperature acoustic-phonon bunching in WS₂/WSe₂ hetero-structure

Abstract The nature of inter-layer optical phonons observed in the hetero-structure is being reported in this work. Additionally, phonon bunching between modes of both and can be ascertained in the acoustic region. The second-order bunching factor, , is seen to improve sharply upon reduction of temperature, below a critical temperature. Moreover, the integral intensity of the peaks increases almost exponentially with the applied power of the laser source. To a good approximation, the phonon frequency corresponding to most of the Raman active modes varies linearly with altered temperature (78–300 K). However, the mixed mode located at exhibits a non-linear temperature dependence over the working range of temperature. Prevailing phonon bunching aspects of the phonon replica discussed in terms of bunching factor, frequency correlation parameter, etc., are highlighted based on acquired low-temperature Raman data and theoretical analogy.