Electron-phonon coupling and monopolar charge fluctuations in intermediate valence TmSe

Polarized Raman spectra of intermediate valence Tm_xSe (x=0.95, 1.00, 1.01) have been measured. The scattering intensity is interpreted in terms of a one-phonon density of states weighted by the electron-phonon matrix element. The latter is described in a model of phonon-induced local, intraionic charge deformabilities. In the symmetry-analysed Raman intensities of A_1g character, two peaks near 8.8meV and 21.9meV are attributed to monopolar charge deformations of the valence-fluctuating Tm ions.