Raman study of coupled electronic and phononic excitations in LuB12

TL;DR

This study investigates the coupled electronic and phononic excitations in LuB12 using Raman spectroscopy, revealing electron-phonon interactions, temperature effects, and estimating the coupling constant relevant for superconductivity.

Contribution

It provides a detailed analysis of electron-phonon coupling in LuB12 through combined experimental Raman data and theoretical simulations, including the determination of the coupling constant.

Findings

Identification of a broad electronic continuum in spectra

Observation of Fano interference due to electron-phonon coupling

Estimated electron-phonon coupling constant λ_ep=0.32

Abstract

Electronic Raman scattering and optical phonon self-energies are studied on single crystals of $LuB_{12}$ with different isotopic composition in the temperature region 10-650K and at pressures up to 10 GPa. The shape and energy position of the spectral peaks depend on the magnitude of the probed wave vector, temperature, and symmetry of excitations. We simulated experimental spectra using electronic structure obtained in the density function theory and taking into account the electron-phonon scattering. The emergence of a broad continuum in the spectra is identified with the inelastic scattering of light from the electronic intraband excitations. Their coupling to non-fully symmetric phonon modes is the source of both the Fano interference and temperature-dependent phonon self-energies. In addition, long wavelength vibrations of the boron atoms are in nonadiabatic regime, so the electronic contribution to their self-energies provides a temperature dependence that is similar to the anharmonic contribution. Comparison of calculation and experiment allowed us to determine the coupling constant $\lambda_{ep}$=0.32, which gives correct critical temperature of the transition to the superconducting state.