Pseudogap state and superconducting state in high- Tc cuprates: anomalous properties in the observed quantities

Abstract

We theoretically investigate the anomalous properties of under-doped high- T c cuprates, both in the normal state and in the superconducting state. We especially pay attention to the pseudogap phenomena in the normal state and their relationship with the superconductivity. We have shown in our previous paper that the pseudogap phenomena are naturally understood as a precursor of the strong coupling superconductivity. We extend our scenario to the superconducting state and discuss the close relationship between the pseudogap state and the superconducting state. The calculation is carried out by using the self-consistent T-matrix approximation. Once the superconducting phase transition occurs, the superconducting fluctuations are suppressed, and the order parameter rapidly grows. With the growth of the order parameter, the gap structure, which is broad in the pseudogap state, becomes sharp. This transition is continuous but rapid. The characteristic scale of the gap is the same, as is directly observed in the spectroscopic measurements. The characteristic features also appear in the several other measurements. We further carry out the definite calculation on the NMR and transport, which show the pseudogap anomaly in the normal state. We investigate their behaviors both in the pseudogap state and in the superconducting state.