Signatures of exchange correlations in the thermopower of quantum dots

TL;DR

This paper investigates how exchange interactions affect the thermopower in quantum dots, revealing characteristic splittings and proposing experimental methods to measure exchange strength.

Contribution

It introduces a many-body rate-equation approach to analyze exchange effects on thermopower, including the impact of cotunneling and a method to determine exchange interaction strength.

Findings

Exchange interaction causes splitting of thermopower quantum jumps.

Splitting depends on electron parity and ground-state spin.

Signatures of exchange correlations persist despite cotunneling effects.

Abstract

We use a many-body rate-equation approach to calculate the thermopower of a quantum dot in the presence of an exchange interaction. At temperatures much smaller than the single-particle level spacing, the known quantum jumps (discontinuities) in the thermopower are split by the exchange interaction. The origin and nature of the splitting are elucidated with a simple physical argument based on the nature of the intermediate excited state in the sequential tunneling approach. We show that this splitting is sensitive to the number parity of electrons in the dot and the dot's ground-state spin. These effects are suppressed when cotunneling dominates the electrical and thermal conductances. We calculate the thermopower in the presence of elastic cotunneling, and show that some signatures of exchange correlations should still be observed with current experimental methods. In particular, we propose a method to determine the strength of the exchange interaction from measurements of the thermopower.