Multiphonon Raman Scattering in Transition Metal Dichalcogenide Double Layers

Abstract

Herein, multiphonon Raman scattering assisted by the interlayer excitons in double transition metal chalcogenide (TMD) layers based on the Huang–Rhys's model is studied. The processes of multiple longitudinal optical (LO) phonons Raman scattering are presented due to the strong exciton–LO phonon coupling. It is found that the Raman scattering intensity and orders of LO phonon overtones depend on the obtained value of Huang–Rhys factor, which can be tuned obviously by the strength of exciton–LO phonon coupling and interlayer distance between two TMD layers. Meanwhile, temperature dependence of scattering intensities for different orders of LO phonon overtones in the multiphonon processes is discussed. The theoretical results provide significant insight not only for the analysis of multiphonon Raman spectroscopy in experiments, but also for the modulation of optical properties in a series of TMD double layers and Van der Waals heterostructures.

Quantum Phase Transitions of Interlayer Excitons in van der Waals Heterostructures

“…Both of them display the discrepancies of the lattice relaxation effect between LST and HST, which also could be evaluated quantificationally by the well-known Huang-Rhys factors given in Table S2, Supporting Information. In fact, self-trapped exciton states arising from the strong coupling between the excitons and phonons lead to a number of phonon replicas, which have been observed in many optical experiments, such as the LO phonon replicas of free excitons and neutral donor-bound excitons, [50][51][52] as well as MRS. [53][54][55][56][57][58] In particular, the strength of excitonphonon coupling, the lattice distortion, and the change in vibrational modes can be directly evaluated by MRS. However, what puzzle is that MRS can also be induced by FS in many past experiments.…”