SUPERCONDUCTIVITY AND DYNAMICAL SHORT-RANGE ORDER IN HIGH-T-C SYSTEMS

We analyze the doping and temperature dependence of the quasi-particle excitation spectrum of the 2D one hand Hubbard model in the normal an d superconducting state using the fluctuation exchange approximation. It is shown that above T-c shadow stales resulting form short-range an tiferromagnetic correlations occur with small but finite excitation en ergies which decrease for decreasing doping, reflecting as dynamically broken symmetry with increasing lifetime. Simultaneously, the intensi ty of these new states increases, the quasi-particle dispersion is str ongly flattened, and a pseudogap in the density of states occurs. With in the superconducting state, we find that the gap function Delta(k) h as d(x2-y2) is symmetry. Furthermore, our results for the spectral den sity explain the dip structures found in photoemission and tunneling e xperiments. These fine structures result from an enhancement of the sc attering rate of shadow states slightly above the superconducting gap.