Cross thermoelectric coupling in normal-superconductor quantum dots

TL;DR

This paper investigates how thermal gradients influence nonlinear electrical responses in a quantum dot system coupled to normal and superconducting leads, revealing tunable effects beyond linear response due to Andreev bound states and quasiparticle tunneling.

Contribution

It demonstrates the impact of thermal gradients on nonlinear current and thermoelectric effects in a normal-superconductor quantum dot system, highlighting the role of Andreev bound states and quasiparticle tunneling.

Findings

Thermal gradients shift Andreev bound states affecting current-voltage characteristics.

Thermoelectric response vanishes under particle-hole symmetry but can be tuned with temperature bias.

Quasiparticle tunneling enhances thermopower sensitivity.

Abstract

We discuss the nonlinear current of an interacting quantum dot coupled to normal and superconducting reservoirs with applied voltage and temperature differences. Due to the particle-hole symmetry introduced by the superconducting lead, the pure (subgap) thermoelectric response vanishes. However, we show that the Andreev bound states shift as the thermal gradient increases. As a consequence, the $I$--$V$ characteristic can be tuned with a temperature bias if the system is simultaneously voltage biased. This is a cross effect that occurs beyond linear response only. Furthermore, we emphasize the role of quasiparticle tunneling processes in the generation of high thermopower sensitivities.