Effect of the Kondo correlation on thermopower in a Quantum Dot.pdf

Effect of the Kondo correlation on thermopower in a Quantum Dot Bing Dong and X. L. Lei Department of Physics, Shanghai Jiaotong University, 1954 Huashan Road, Shanghai 200030, P. R. China In this paper we study the thermopower of a quantum dot connected to two leads in the presence of 2 Kondo correlation by employing a modified second-order perturbation scheme at nonequilibrium. A 0 simple scheme, Ng’s ansatz [Phys. Rev. Lett. 76, 487 (1996)], is adopted to calculate nonequilibrium 0 distribution Green’s function and its validity is further checked with regard to the Onsager relation. 2 Numerical results demonstrate that the sign of the thermopower can be changed by tuning the t energy level of the quantum dot, leading to a oscillatory behavior with a suppressed magnitude c due to the Kondo effect. We also calculate the thermal conductance of the system, and find that O the Wiedemann-Franz law is obeyed at low temperature but violated with increasing temperature, corresponding to emerging and quenching of the Kondo effect. 2 PACS numbers: 72.10.Fk, 72.15.Qm, 72.20.Pa, 73.23.Hk ] l l a h - I. INTRODUCTION s e m Observation of the Kondo effect in a semiconductor quantum dot (QD)1,2 which provided a testing ground of the . quantum behavior of electron wave functions and many-body effects, has stimulated a great deal of experimental3,4 t a and theoretical5–9 investigation. So far, many interesting features in QD, such as Kondo-assisted enhancement m of conductance, its sp