Pseudogap induced by superconducting fluctuation and anomalous metals in high-Tc superconducting materials

The pseudogap in the single particle spectrum induced by the superconducting fluctuation together with the antiferromagnetic spin fluctuation has been believed to play key roles to determine essential features of anomalous properties of Cu-oxide high-T-c superconducting materials observed at temperatures higher than the superconducting transition temperature T-c. The roles are described as follows: in metals near Mott insulators, doped holes create new states inside the charge transfer gap called as ingap states, which have band width proportional to the hole doping rate delta and interact with each other through the superexchange interaction J(s) enhanced by the antiferromagnetic spin fluctuation. This effective interaction promotes super conducting fluctuation, which induces a pseudogap in the single particle spectra. On the other hand. the pseudogap suppresses the spin fluctuation. Thus. effects of both of the spin fluctuation and the superconducting fluctuation need to be treated in a consistent way. In an underdoped system. the spin fluctuation dominates at higher temperatures. while the superconducting fluctuation or the pseudogap effect dominates at lower temperatures above T-c. This competition determines the anomalous temperature dependence of systems. We demonstrate the senario explicitly by taking the d-p model with the help of the 1/N-expansion theory and calculating T-c, the NMR relaxation rate 1/T-I and the single-particle spectrum. (C) 2000 Elsevier Science Ltd. All rights reserved.