Theory on pseudogap state and superconducting state in strong coupling superconductors

The relation between the pseudogap state and the superconducting phase in s trong coupling superconductors (like cuprates and organics) is investigated by extending the self-consistent T-matrix approximation below the transiti on temperature (T-c). The superconducting order parameter is obtained by so lving the gap equation which includes the superconducting fluctuation in a self-consistent way; the fluctuation causes the pseudogap behavior above T- c. The rapid growth of the order parameter below T-c, is found to be a char acteristic feature of the strong coupling superconductors. As a result of t he rapid growth of the order parameter, the spectral density at the Fermi l evel in the one-particle spectrum rapidly decreases and that at the peak po sition sharply grows as soon as the system goes into the superconducting st ate. These observations are consistent with angle-resolved photoemission sp ectroscopy experiments. The properties of the one-particle spectrum above a nd below T-c, are found to be well explained by considering the self-energy correction originating from the superconducting fluctuation and the develo pment of the order parameter.