Resonant Raman scattering of surface phonon polaritons mediated by excitons in WSe$_2$ films

TL;DR

This study explores the interaction between surface phonon polaritons and excitons in hBN/WSe2 heterostructures using resonant Raman spectroscopy, revealing how excitons influence phonon polariton signals and their dependence on layer thickness.

Contribution

It demonstrates that WSe2 excitons can mediate resonant Raman scattering of surface phonon polaritons in hBN, providing new insights into exciton-polariton interactions in van der Waals heterostructures.

Findings

Resonant Raman signals are enhanced when photon energy matches WSe2 excitons.

The SPhP Raman bandwidth depends on hBN layer thickness.

Momentum non-conserving scattering explains experimental data.

Abstract

Surface phonon-polaritons propagating along interfaces of polar dielectrics coexist with excitons in many van der Waals heterostructures, so understanding their mutual interactions is of great interest. Here, we investigate the type I surface phonon polariton of hBN via low-temperature resonant-Raman spectroscopy in hBN/WSe2 heterostructures. The resonantly enhanced hBN surface phonon polariton (SPhP) Raman signal, when laser energy is such that the scattered photons have energy close to that of the WSe2 excitons, enables detailed characterization of type I SPhP in hBN even when hBN is one monolayer thick. We find that the measured bandwidth of the SPhP Raman signal depends on the thicknesses of the hBN layer. We are able explain the experimental data using transfer matrix method simulations of SPhP dispersions providing that we assume the Raman scattering to be momentum non-conserving, as could be the case if localized WSe2 exciton states participated in the process. We further show that resonant Raman scattering from SiO2 SPhP can also be mediated by WSe$_2$.