Thermal conductance of a weakly coupled quantum dot

TL;DR

This paper investigates the electronic thermal conductance in a weakly coupled quantum dot, revealing oscillations related to Coulomb blockade and a breakdown of the Wiedemann-Franz law in the quantum limit, with implications for thermoelectric efficiency.

Contribution

It derives a linear response model for heat current in quantum dots and uncovers the oscillatory behavior and quantum limit suppression of thermal conductance, challenging classical laws.

Findings

Thermal conductance oscillates with Fermi energy.

In the quantum limit, conductance peaks tend to zero exponentially.

Wiedemann-Franz law fails in the quantum regime, but is recovered classically.

Abstract

We calculate the electronic contribution to the thermal conductance in a quantum dot that is weakly coupled via tunnel barriers to two electrons reservoirs. A linear response model is derived for the calculation of the heat current Q through the quantum dot when a small temperature difference and a small voltage difference are applied between the two reservoirs. We find that the thermal conductance oscillates as a function of the Fermi energy. The periodicity of these oscillations is the same as this of the Coulomb blockade oscillations of the conductance. In the quantum limit the peak values of the thermal conductance tends to zero as exp(-DE/kT) where DE is the spacing between the energy levels in the dot. This surprising result implies the failure of the Wiedemann-Franz law in the quantum limit and it could lead to structures with large figure of merit ZT. We have also examined the behavior of the thermal conductance in the classical limit and we find that the Wiedemann-Franz is recovered.