Phonon spectral function for an interacting electron-phonon system

TL;DR

This paper uses exact diagonalization to analyze how electron-electron interactions influence phonon spectral functions, revealing changes in phonon spectral width and mode coupling transfer, which help explain experimental differences in electron-phonon coupling estimates.

Contribution

It provides a detailed numerical study of electron-phonon interactions considering Coulomb repulsion, highlighting spectral and mode transfer effects not previously characterized.

Findings

Spectral width of phonons decreases with increasing Coulomb interaction U.

Coupling transfer from upper to lower phonon mode occurs and diminishes as U increases.

Results explain differences between Raman and photoemission measurements of electron-phonon coupling.

Abstract

Using exact diagonalzation techniques, we study a model of interacting electrons and phonons. The spectral width of the phonons is found to be reduced as the Coulomb interaction U is increased. For a system with two modes per site, we find a transfer of coupling strength from the upper to the lower mode. This transfer is reduced as U is increased. These results give a qualitative explanation of differences between Raman and photoemission estimates of the electron-phonon coupling constants for A3C60 (A= K, Rb).