Nernst coefficient and Magnetoresistance in High-Tc Superconductors

TL;DR

This study explains the drastic increase in Nernst coefficient and magnetoresistance below T* in high-Tc cuprates as a consequence of superconducting fluctuations mediated by antiferromagnetic correlations, without invoking vortices.

Contribution

It introduces a theoretical framework using FLEX+T-matrix approximation to explain transport phenomena in the pseudo-gap region of high-Tc cuprates, emphasizing the role of vertex corrections.

Findings

Transport anomalies are explained by enhanced superconducting fluctuations.

The pseudo-gap region is described as a Fermi liquid with AF and SC fluctuations.

Vortex excitation is not necessary to account for the observed behaviors.

Abstract

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.