Electron-Phonon Effects in the Infrared Properties of Metals

Abstract

Electron-phonon contributions to the infrared absorption in metals are examined from two points of view. First, "golden-rule" calculations are given for normal metals and superconductors which reproduce the phenomenological theory used by Joyce and Richards to analyze their data in lead. This theory is expected to be valid for weak electron-phonon coupling. Second, the Holstein transport theory for normal metals is used to examine the corrections arising from strong coupling. Solutions are found for the response function at general frequencies and wave vectors. The results are similar in form to the golden-rule theory, and provide a simple correction factor to this theory. It is suggested that optical measurements on both normal and superconducting materials may provide a valuable tool for analyzing the coupled electron-phonon system.