Effect of the Kondo correlation on thermopower in a Quantum Dot

TL;DR

This study investigates how Kondo correlations influence the thermopower in a quantum dot system, revealing oscillatory behavior and temperature-dependent violations of the Wiedemann-Franz law.

Contribution

It introduces a modified second-order perturbation scheme to analyze nonequilibrium thermopower in quantum dots with Kondo effects, validating the approach with Onsager relation checks.

Findings

Thermopower sign can be tuned by adjusting the quantum dot energy level.

Kondo effect causes oscillations and suppression in thermopower magnitude.

Wiedemann-Franz law holds at low temperatures but breaks down at higher temperatures.

Abstract

In this paper we study the thermopower of a quantum dot connected to two leads in the presence of Kondo correlation by employing a modified second-order perturbation scheme at nonequilibrium. A simple scheme, Ng's ansatz [Phys. Rev. Lett. {\bf 76}, 487 (1996)], is adopted to calculate nonequilibrium distribution Green's function and its validity is further checked with regard to the Onsager relation. Numerical results demonstrate that the sign of the thermopower can be changed by tuning the energy level of the quantum dot, leading to a oscillatory behavior with a suppressed magnitude due to the Kondo effect. We also calculate the thermal conductance of the system, and find that the Wiedemann-Franz law is obeyed at low temperature but violated with increasing temperature, corresponding to emerging and quenching of the Kondo effect.