Infrared reflectivity spectroscopy of electron-phonon interactions

Abstract

The crucial role of electron-phonon interactions and their signatures in optical conductivity deduced from the analysis of infrared-visible reflection spectra is reviewed. The usefulness of a general phenomenological model able to describe the couplings of phonons, polarons, plasmon, superconducting condensate, is discussed. Among other examples of applications, the problem of the signature of Cooper pair condensation in the superconducting phase of high-T c cuprates is discussed in the framework of London and Mattis-Bardeen models.

Optical conductivity of high-Tccuprate thin films deposited by multi-target laser ablation

“….) [25,26,[29][30][31][32][33][34][35][36][37][38][39]. In the presence of oscillators and plasmon in the same frequency range, the following expression (double-damping Drude model [30][31][32]37]) has been shown to allow the separate determination of phonons (or oscillators of another type) and plasmon parameters…”

“…On the other hand, the charge carrier concentration is high enough in all films to screen the phonons, largely or almost completely. By comparison with the spectra of cuprate single crystal samples [9,26,32,36,40] for the polarization parallel to the c axis which shows the sole response to unscreened phonons, epitaxy of the films is most likely achieved. Phonons indeed are highly screened in films that display superconductivity.…”

“…But actually, all conducting oxides, not only cuprates or oxides of transition metals but also others, seem to deviate from conventional metal descriptions (see e.g. the review papers [25], [26]). The phenomenon is even more general since other nonmetallic materials like conducting polymers also show strong deviations from conventional Drude behaviour [27].…”

“…The desired model should allow a parametrization of any conductivity spectrum to allow subsequent comparison of the electronic properties of oxides belonging to different families. The purpose of this paper is to show that a 'double-damping' Drude model, already found to fit the spectral conductivity of a wide variety of oxides [25,26,[28][29][30][31][32][33][34][35][36][37][38], applies to cuprate thin films equally well.…”