Theory of pseudogap phenomena in high-T-c cuprates based on the strong coupling superconductivity

In this paper we study the effects of the strong coupling superconductivity on the normal state electronic structure. We point out that the pseudogap phenomena in High-T-c cuprates are naturally explained as a precursor of th e strong coupling superconductivity We expand the reciprocal of the T-matri x with respect to the momentum and the frequency, and we discuss the proper ties of the expansion parameters. We estimate these parameters and carry ou t the calculations for the single particle self-energy using the T-matrix a nd the self-consistent T-matrix approximations, respectively. We show that the superconducting fluctuations, which are strongly diffusive within the c onventional weak coupling theory, become propagative and have the character of the pre-formed pairs in the strong coupling case. The spectral weight a nd the density of states show the gap-like features by the effects of the r esonances with the thermally excited weakly-damped pre-formed pairs. The sp ectral weight at the Fermi energy is strongly suppressed. This suppression starts at the mean field critical temperature T-MF and the actual critical temperature T-c is strongly reduced owing to the fluctuations. These featur es properly explain to the pseudogap phenomena in High-T-c cuprates.