Theory on superconducting transition from pseudogap state

The anomalous properties of High-T-c cuprates are investigated both in the normal state and in the superconducting state. In particular, we pay attent ion to the pseudogap in the normal state and the phase transition from the pseudogap state to the superconducting state. The pseudogap phenomena obser ved in cuprates are naturally understood as a precursor of the strong coupl ing superconductivity. We have previously shown by using the self-consisten t T-matrix calculation that the pseudogap is a result of the strong superco nducting fluctuations which are accompanied by the strong coupling supercon ductivity in quasi-tyro dimensional systems [J. Phys. Sec. Jpn. 68 (1999) 2 999]. We extend the scenario to the superconducting state. The close relati on between the pseudogap state and the superconducting state is pointed out . Once the superconducting phase transition occurs, the superconducting ord er parameter rapidly grows rather than the result of BCS theory. With the r apid growth of the order parameter, the gap structure becomes sharp, while it is remarkably broad in the pseudogap state. The characteristic energy sc ale of the gap does not change. These results well explain the phase transi tion observed in the spectroscopic measurements. Further, we calculate the magnetic and transport properties which show the pseudogap phenomena. The c omprehensive understanding of the NMR, the neutron scattering, the optical conductivity and the London penetration depth is obtained both in the pseud ogap state and in the superconducting state.