Single-Particle Excitations in a Two-Dimensional Strong-Coupling Superconductor

We present calculations of the single-particle excitation spectrum for a 2D strong-coupling superconductor in a conserving approximation. Spectral weight at low frequency is substantially reduced as the superconducting transition is approached from the normal state. The suppression of low-energy excitations is a consequence of Cooper-pair fluctuations that are described self-consistently in the fluctuation exchange approximation. The static and uniform electromagnetic response provides a measure of the super fluid density and a fully selfconsistent indication of the superconducting transition temperature. The pseudogap observed in the normal state of the high-temperature superconductors has focused interest on fluctuations directly associated with superconductivity (Emery and Kivelson 1995, Randeria, et al. 1992, Doniach and Inui 1990). The occurrence of superconductivity in two-dimensional copper-oxide layers encourages speculation that Cooper-pair fluctuations affect the low-energy excitation spectrum irrespective of the pairing mechanism