Thermal Transport and Non-Mechanical Forces in Metals

TL;DR

This paper explores the thermopower in electron fluids, proposing it is determined by entropy per particle due to an entropic force from coupling heat and mass currents, and clarifies a recent exact solution method for electronic transport.

Contribution

It introduces a thermodynamic perspective on thermopower and clarifies the role of entropic forces, extending understanding of electronic transport in metals.

Findings

Thermopower is linked to entropy per particle.

An entropic force couples heat and mass currents.

Clarification of an exact low-temperature transport solution.

Abstract

We discuss contributions to the thermopower in an electron fluid. A simple argument based on Newton's second law with the pressure gradient as the force suggests that the thermopower is given by a thermodynamic derivative, viz., the entropy per particle, rather than being an independent transport coefficient. The resolution is the existence of an entropic force that results from a coupling between the mass current and the heat current in the fluid. We also discuss and clarify some aspects of a recent paper (Phys. Rev. B {\bf 102}, 214306 (2020)) that provided a method for exactly solving electronic transport equations in the low-temperature limit.