Influences of electron-phonon interaction on the thermoelectric effect in a parallel double quantum dot system

Abstract

A quantum-dot system is a typical low-dimensional system, and previous researches showed that its thermoelectric conversion efficiency can be markedy improved due to its unique physical properties. In this poper, we choose the parallel double-quantum-dot structure and discuss the influence of the electron-phonon interaction on the thermoelectric-related parameters, i.e., the electric conductance, thermopower, the figure of merit, and thermal conductance, by using the nonequilibrium Green's function method. Our theoretical calculation results show that under the condition of low temperature, the occurrence of the Fano interference can assist to enhance the thermoelectric effect. When the electron-phonon interaction is taken into account, it can suppress the electric and thermal conductances to a certain extent because of its negative effect on the Fano interterence. However, we readily find that apparently the strengthening of the electron-phonon interaction cannot suppress the maximum of the thermopower. Instead, in some regions, the thermopower has an opportunity to enhance due to the appearance of a new channel caused by the electron-phonon interaction. Meanwhile, the figure of merit is found to cause similar effects to the thermopower. Therefore, in the case of low temperature, the electron-phonon interaction contributes little to the destruction of the thermoelectric effect, namely, it is not the necessary condition for the suppression of the thermoelectric effect. With the increase of temperature, the negative effect of the electron-phonon interaction on the Fano interference becomes relatively distinct, which inevitably weakens the thermoelectric effect. Results of this paper will help to clarify the influence of electron-phonon interaction on the thermoelectric effect.