Strong coupling effects in highz. sbnd; Tc oxides from paramagnons

Abstract

While it is acknowledged, from both theoretical and experimental considerations, that the electron-phonon mechanism is not responsible for the superconductivity in the high z. sbnd; T c oxides, several experiments remain which exhibit strong-coupling effects. This paradox can be resolved by considering a mechanism for the high z. sbnd; T c oxides which is mainly electronic in origin but with a small contribution from the electron-phonon interaction and a significant contribution from dynamic spin fluctuations, paramagnons. In such a model, strong coupling effects can arise from the paramagnons. Fixing the electron-phonon contribution to achieve an isotope effect coefficient of 0.05 at a T c of 96K, we can obtain a large gap ratio, 2 Δ 0/ k B T c , a two-fluid model-like temperature dependence for the penetration depth, and a featureless optical conductivity, σ S / σ N , in agreement with interpretation of experiment.