Electronic Raman scattering and the electron-phonon interaction in YB$_6$

Electronic Raman scattering in YB$_6$ and in its structural and electronic analog LaB$_6$ has been studied in the temperature range of $10$–$730$ K. The experimental spectra have been compared to those calculated on the basis of ab initio band structures with renormalization owing to the electron-phonon interaction. Good agreement between the calculation and experiment for LaB$_6$ has been obtained throughout the entire temperature range. This allows the determination of the coupling constant $\lambda_{ep}=0.25$. To satisfactorily describe the spectra of electronic light scattering in YB$_6$, it is necessary to introduce an additional electron relaxation channel. In this case, the estimate of the electron-phonon coupling constant $\lambda_{ep}$ is no more than $0.4$; for this reason, a high superconducting transition temperature cannot be explained only by the phonon mechanism.