Multiphonon Raman Scattering and Strong Electron-Phonon Coupling in 2D Ternary Cu₂MoS₄ Nanoflakes

The interaction between photogenerated carriers with lattice vibrations plays a fundamental role in the nonradiative recombination and charge-transfer processes occurring in photocatalysis and photovoltaics. Here, we employ Raman spectroscopy to investigate the electron-phonon interaction in ternary layered Cu₂MoS₄ nanoflakes. Multiphonon Raman scattering with up to fourth-order longitudinal optical (LO) overtones is observed under above-band gap excitation, indicating a strong electron-phonon coupling (EPC) that could be described by the cascade model. The Huang-Rhys factor was derived to characterize the strength of EPC and was found to be increasing with decreasing temperature. First-principles calculations of lattice dynamics and electron-phonon matrix elements suggest that the strong EPC in Cu₂MoS₄ is dominated by Fröhlich coupling between electron and the electric fields, which is induced by the localized phonon mode originating from a flat phonon branch. Our findings facilitate the understanding of electron-phonon interaction in 2D ternary Cu₂MoS₄ and pave the way for developing and optimizing optoelectronic devices.