Theoretical Study of Anomalous Metallic Propertices of Strongly Coupled Electrons.

点击翻译按钮获取中文摘要

The pseudpgap 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 δ and interact with each other through the superexchange interaction J_s enhanced by the antiferromagnetic spin fluctuation. This effective interaction promotes superconducting 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 have demonstrated the senario to work 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_1 and the single-particle spectra. We have treated the spin fluctuation in the renormalized random phase approximation and the superconducting fluctuation in the renormalized t-matrix approximation, where the effective pairing interactions are mediated by the renormalized spin fluctuation.