Superconductivity and dynamical short-range order in high- Tc systems

Abstract

We analyze the doping and temperature dependence of the quasi-particle excitation spectrum of the 2D one hand Hubbard model in the normal and superconducting state using the fluctuation exchange approximation. It is shown that above T c shadow states resulting form short-range antiferromagnetic correlations occur with small but finite excitation energies which decrease for decreasing doping, reflecting as dynamically broken symmetry with increasing lifetime. Simultaneously, the intensity of these new states increases, the quasi-particle dispersion is strongly flattened, and a pseudogap in the density of states occurs. Within the superconducting state, we find that the gap function Δ k has d x 2 - y 2 is symmetry. Furthermore, our results for the spectral density explain the dip structures found in photoemission and tunneling experiments. These fine structures result from an enhancement of the scattering rate at shadow states slightly above the superconducting gap.