Thermoelectric power and electron–phonon enhancement in YBa₂Cu₃O_7–δ

Abstract

The recent discovery of high-temperature oxide superconductors^1–4 has generated enormous interest both among physicists and, because of their obvious technological importance, in the wider community. One of the less-studied but potentially interesting properties is the thermoelectric power (or thermopower), which is the coefficient that characterizes the electromotive force resulting from the redistribution of electrons in a temperature gradient. The temperature dependence of the thermopower is modified by the electron-phonon interaction, and provides a means of estimating the strength of the interaction. We have performed measurements on several samples of YBa₂Cu₃O_7–δ, and find an unexpected precursor effect just above the transition temperture T_c—namely, an increase rather than decrease in thermopower. The measured thermopower is positive with a magnitude typical of metallic conductors, and shows some similarity to the calculated diffusion thermopower for a reltively large electron-phonon coupling parameter of λ≈ 2.5.