Non-linear Nernst effect in bilayer WTe$_2$

TL;DR

This paper derives a theoretical framework for the non-linear anomalous Nernst effect (NLANE), demonstrating its dependence on Berry curvature and applying it to bilayer WTe$_2$ to predict experimental signatures.

Contribution

The paper provides the first derivation of the non-linear Nernst coefficient as a second-order response and applies it to bilayer WTe$_2$, revealing tunable sign changes and specific experimental predictions.

Findings

NLANE arises from Berry curvature near the Fermi surface.

Sign of NLANE can be tuned by spin-orbit coupling.

Temperature and chemical potential dependencies are characterized.

Abstract

Unlike the conventional (linear) anomalous Nernst effect, the non-linear anomalous Nernst effect (NLANE) can survive in an inversion symmetry broken system even in the presence of time-reversal symmetry. Using semiclassical Boltzmann transport theory, we derive the general expression of the non-linear anomalous Nernst coefficient as the second-order response function to the applied temperature gradient. We find that the non-linear Nernst current, which flows perpendicular to the temperature gradient even in the absence of a magnetic field, arises due to the Berry curvature of the states near the Fermi surface, and thus is associated with purely a Fermi surface contribution. We apply these results to bilayer WTe$_2$, which is an inversion broken but time reversal symmetric type-II Weyl semimetal supporting chiral Weyl fermions. By tuning the spin-orbit coupling, we show that the sign of the NLANE can change in this system. Together with the angular dependence, we calculate the temperature and chemical potential dependencies of NLANE in bilayer WTe$_2$, and predict specific experimental signatures that can be checked in experiments.