Theory on Pseudogap State and Superconducting State in Strong Coupling Superconductors

Abstract

The relation between the pseudogap state and the superconducting phase in strong coupling superconductors (like cuprates and organics) is investigated by extending the self-consistent T-matrix approximation below the transition temperature ( T c ). The superconducting order parameter is obtained by solving 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 characteristic feature of the strong coupling superconductors. As a result of the rapid growth of the order parameter, the spectral density at the Fermi level in the one-particle spectrum rapidly decreases and that at the peak position sharply grows as soon as the system goes into the superconducting state. These observations are consistent with angle-resolved photoemission spectroscopy experiments. The properties of the one-particle spectrum above and below T c are found to be well explained...