The Effects Of Electron-phonon Interaction On Electron Transport And Thermoelectric Effect In Quantum Dots

With the remarkable advances in the ability to fabricate nanostructures, thermoelectric properties of solid-state filed, typically in the case of quantum dots, have been attracted many researchers’ eyes. This work is not only the complement of basic theory, but also provides theoretical basis for the development of quantum device. Coupling between the electronic and vibrational degrees of freedom can significantly affect the performance of the systems fabricated from QDs.In this paper, by combining the nonequilibrium Keldysh Green’s-function technique with the canonical transformation for the electron-phonon system, we intend to study the thermoelectric effect through the quantum dot in the presence of strong local electron-phonon interaction (EPI). We choose the parallel double quantum dots system and the three-terminal quantum dot with one normal lead and two ferromagnetic leads, respectively. The work focuses analyzing and comparing electronic conductance, thermal conductance, thermopower and ZT, getting some meaningful results finally. We introduce our works briefly from two aspects as follows:On the one hand, we discuss the effects of the EPI on the parallel double quantum dots system by adding magnetic fields Φ=0in the QDs. Under different environmental parameters and EPI strengths, we get some meaningful results. It is found that the EPI destroys the electron transport. In the presence of EPI, the position of the peaks in the spectrum of electrical conductance and thermal conductance is restrained. However, the spectrums of thermopower and ZT appear different performances. Extra peaks are clearly observed in the ZT spectrums resulting from the phonon-assisted tunneling. Indeed, the EPI results in the creation of the new channels for the electron transport. In the case of Φ=π, the influences of the EPI are more obvious.On the other hand, we choose the three-terminal quantum dot with one normal lead and two ferromagnetic leads system. Effect of EPI on the conductance coefficients are analyzed.We find that the EPI leads to the appearance of the extra peaks in thermopower spectrum and the increasement of the ZT. In addition, we consider the system in the case of non-linear region, EPI effect on this part is more complicated. In the nonlinear region, EPI on the thermoelectric effect system play an active role with two ferromagnetic leads system. The influences of the EPI on the thermoelectric properties, a serially coupled double quantum dots system weakly attached to metallic leads is negative.