Conductivity below Tc in high-temperature superconductors

Quasiparticle damping due to electron-electron scattering in a system with a nested Fermi surface is calculated with an isotropic energy gap 2Δ. Below the superconducting critical temperature, the scattering rate is largely reduced, with an anomalous temperature variation and a roughly linear frequency dependence above a threshold of 3Δ. This damping leads to an enhanced coherence peak in the conductivity just below Tc, which agrees with experimental data on YBa2Cu3O7 obtained by Nuss et al. Conventional electron phonon-scattering is found to give a much smaller peak. (orig.)