Theory of electrical transport in the pseudogap state: effects of spin fluctuations and superconducting fluctuations

Abstract

Electrical transport in High- T c superconductors is investigated. The main interest is on the pseudogap state, which is induced by the superconducting (SC) fluctuations. The electric transport shows a characteristic behavior in the pseudogap state, which is considerably different from the magnetic and single-particle properties. We show that these properties are comprehensively explained by taking into account the spin fluctuations and SC fluctuations simultaneously. It is pointed out that the characteristic momentum dependences of the system play an essential role in this explanation. We perform the microscopic calculation to describe the SC fluctuations and pseudogap phenomena, starting from the repulsive Hubbard model. This is the self-consistent FLEX+ T-matrix approximation in which the spin fluctuations, SC fluctuations and their effects on the single-particle self-energy are determined self-consistently. The longitudinal and transverse conductivities are calculated by using the Éliashberg and Kohno–Yamada formalism. The in-plane and c-axis optical conductivities are also calculated. The effects of the spin fluctuations and SC fluctuations are estimated, respectively. The results clarify the main effect of the SC fluctuations on the transport coefficients and give a consistent understanding with the experimental results.