On the heat current in the magnetic field: Nernst-Ettingshausen effect above the superconducting transition

TL;DR

This paper revises calculations of the Nernst-Ettingshausen effect above the superconducting transition by including the magnetic term in the heat current operator, showing fluctuations do not alter particle-hole asymmetry and that large effects in cuprates are due to vortex-like excitations.

Contribution

It introduces a gauge-invariant approach to calculating thermomagnetic effects above the superconducting transition, emphasizing the role of phase fluctuations in high-$T_c$ cuprates.

Findings

Fluctuations of the order parameter modulus do not affect particle-hole asymmetry.

Thermomagnetic effects are proportional to the square of PHA and are small.

Vortex-like excitations are needed to explain large Nernst signals in cuprates.

Abstract

For maintaining gauge invariance in a magnetic field, the heat current operator should include the magnetic term. Taking this term into account, we revised calculations of the Nernst-Ettingshausen effect above the superconducting transition. We found that the fluctuations of the modulus of the order parameter do not change the particle-hole asymmetry (PHA) of the thermomagnetic effects. As in the normal state, the thermomagnetic effects in the fluctuation region are proportional to the square of PHA and, therefore, small. Large Nernst effect observed in the high-$T_c$ cuprates requires vortex-like excitations due to the phase fluctuations, which are beyond the Gaussian-fluctuation theory.