Universality and the thermoelectric transport properties of a double quantum dot system: Seeking for conditions that improve the thermoelectric efficiency

TL;DR

This paper investigates conditions for optimizing thermoelectric efficiency in quantum dot systems, highlighting the role of quantum phase shifts, charge fluctuations, and bound states in the continuum, with implications for experimental realization.

Contribution

It identifies specific conditions involving quantum phase shifts and bound states that can enhance thermoelectric efficiency in double quantum dot systems, extending previous single-dot analyses.

Findings

Single quantum dots in the Kondo regime cannot reach optimal thermoelectric efficiency.

Maintaining one dot at electron-hole symmetry enables conditions for improved efficiency in double dots.

Presence of bound states in the continuum and quasi-BICs can significantly enhance thermoelectric performance.

Abstract

Employing universal relations for the Onsager coefficients in the linear regime at the symmetric point of the single impurity Anderson model, we calculate the conditions under which the quantum scattering phase shift should satisfy to produce the asymptotic Carnot's limit for the thermoelectric efficiency. We show that a single quantum dot connected by metallic leads at the Kondo regime cannot achieve the conditions that cause the best thermoelectric efficiency. We study a system of serial double quantum dots without inter-dot correlations. We show that maintaining one dot in the electron-hole symmetric point makes it possible to obtain conditions for the quantum phase shift linked to charge fluctuations in the other quantum dot that satisfy the conditions associated with enhancing the thermoelectric efficiency. We also discuss the presence of bound states in the continuum (BICs) and quasi-BICs associated with the quantum scattering interference process that improves thermoelectric efficiency. We identify two types of quasi-BICs that occur at low and high temperatures: The first is associated with single Fano resonances, and the last is with several Fano processes. We also discussed possible temperature values and conditions that could be linked with the experimental realization of our results.