The transport through a quantum dot coupled to the external leads
We study the transport properties of a single level quantum dot connected to the external leads using the nonequilibrium Green's function formalism.
For a description of correlations we consider the single impurity Anderson model. We demonstrate that the electron correlations exemplified by the on-dot (charging) energy U lead to several unique features. The most intriguing one is the observation of the Kondo effects in case the single particle electron level located slightly below Fermi level for low temperatures forms a bound singlet state. We show that the zero bias anomaly of the differential conductance is accompanied by a change of sign of the thermopower below T .
We also study the situation when quantum dot is located between normal and superconducting lead. Some qualitative changes are observed of the charge current by the electron pair coherence.
We investigate the proximity effect in a quantum dot with leads to a particle-hole mixing at small energies . For the only possibility for the charge transport is through the Andreev tunnelling. In presence of the strong on-dot correlations the Kondo states occurs at sufficiently low temperatures. Quantum transport in superconducting devices is thus controlled by the interplay between the Kondo effect and Andreev reflection processes.