Influence of phonon-assisted tunneling on the linear thermoelectric transport through molecular quantum dots

TL;DR

This paper explores how vibrational effects, especially phonon-assisted tunneling, influence thermoelectric transport in molecular quantum dots, revealing conditions for enhanced thermoelectric efficiency at strong coupling.

Contribution

It provides a nonperturbative analysis of phonon effects on thermoelectric transport using NRG and FRG methods, highlighting regimes of enhanced thermoelectric performance.

Findings

Phonon-assisted tunneling significantly affects thermoelectric properties.

Strong electron-phonon coupling can enhance thermoelectric efficiency.

Antiadiabatic regime favors improved thermoelectric performance.

Abstract

We investigate the effect of vibrational degrees of freedom on the linear thermoelectric transport through a single-level quantum dot described by the spinless Anderson-Holstein impurity model. To study the effects of strong electron-phonon coupling, we use the nonperturbative numerical renormalization group approach. We also compare our results, at weak to intermediate coupling, with those obtained by employing the functional renormalization group method, finding good agreement in this parameter regime. When applying a gate voltage at finite temperatures, the inelastic scattering processes, induced by phonon-assisted tunneling, result in an interesting interplay between electrical and thermal transport. We explore different parameter regimes and identify situations for which the thermoelectric power as well as the dimensionless figure of merit are significantly enhanced via a Mahan-Sofo type of mechanism. We show, in particular, that this occurs at strong electron-phonon coupling and in the antiadiabatic regime.