Thermoelectric transport behavior of a series-coupled double quantum dots system with the Kondo Effect

Abstract We study the thermoelectric transport of a series-coupled double quantum dots (SDQDs) system, based on the hierarchical equations of motion approach. The thermocurrent as a function of the energy level of QDs gives rise to a sign-changing phenomenon. The temperature difference between the two leads can enhance the thermocurrent. Moreover, the sign changing also generates in thermocurrent as a function of temperature due to the transition from the many-body Kondo resonant tunneling process to the single electron process of the SDQDs system. The inter-dot coupling strength between two QDs not only affects the value of the thermocurrent but also influences the characteristic temperature at which the sign changing of thermocurrent emerges. In a weak coupling regime, the thermocurrent firstly is enhanced by inter-dot coupling strength due to the ‘ t -enhanced Kondo effect’ and then decreases with inter-dot coupling strength due to the effective antiferromagnetic interaction between the two QDs. In the middle coupling regime, the forming coherence bonding and antibonding orbitals channels and the residual Kondo effect co-dominate the transport process. The thermocurrent firstly decreases, then increases, and finally decreases with temperature. However, the thermocurrent shows a transition from increasing to decreasing behavior with temperature in the strong coupling regime. Although the inter-dot coupling strength t has a complex impact on the SDQDs system, the characteristic temperature k B T c , at which a sign changing appears, indicates a quantitative relationship with the value of the inter-dot coupling strength t by an identical amount of the Kondo correlation being partially destroyed.