Nernst coefficient and Magnetoresistance in High-Tc Superconductors

In hole-doped high-Tc cuprates, the Nernst coefficient (\nu) as well as the magnetoresistance (\Delta\rho/\rho) increase drastically below the pseudo-gap temperature, T^*. This unexpected result attracts much attention in that it reflects the fundamental feature of the electronic state in the pseudo-gap region, which has been a central issue on high-Tc cuprates. In this letter, we study these transport phenomena in terms of the fluctuation-exchange (FLEX)+T-matrix approximation. In this present theory, the d-wave superconducting (SC) fluctuations, which are mediated by antiferromagnetic (AF) correlations, become dominant below T^*. We focus on the role of the vertex corrections both for the charge current and the heat one, which are indispensable to keep the conservation laws. As a result, the mysterious behaviors of \nu and \Delta\rho/\rho, which are the key phenomena in the pseudo-gap region, are naturally explained as the reflection of the enhancement of the SC fluctuation, without assuming thermally excited vortices. The present result suggests that the pseudo-gap region in high-Tc cuprates is well described in terms of the Fermi liquid with AF and SC fluctuations.