Interplay of Kondo and superconducting correlations in the nonequilibrium Andreev transport through a quantum dot

Physical review. B, Condensed matter (Impact Factor: 3.66). 01/2011; 84(7). DOI: 10.1103/PhysRevB.84.075484
Source: arXiv

ABSTRACT Using the modified perturbation theory, we theoretically study the
nonequilibrium Andreev transport through a quantum dot coupled to normal and
superconducting leads (N-QD-S), which is strongly influenced by the Kondo and
superconducting correlations. From the numerical calculation, we find that the
renormalized couplings between the leads and the dot in the equilibrium states
characterize the peak formation in the nonequilibrium differential conductance.
In particular, in the Kondo regime, the enhancement of the Andreev transport
via a Kondo resonance occurs in the differential conductance at a finite bias
voltage, leading to an anomalous peak whose position is given by the
renormalized parameters. In addition to the peak, we show that the energy
levels of the Andreev bound states give rise to other peaks in the differential
conductance in the strongly correlated N-QD-S system. All these features of the
nonequilibrium transport are consistent with those in the recent experimental
results [R. S. Deacon {\it et al.}, Phys. Rev. Lett. {\bf 104}, 076805 (2010);
Phys. Rev. B {\bf 81}, 12308 (2010)]. We also find that the interplay of the
Kondo and superconducting correlations induces an intriguing pinning effect of
the Andreev resonances to the Fermi level and its counter position.

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