报告摘要
| We investigate theoretically the Andreev transport through a quantum dot strongly coupled with a normal metal/ferromagnet and a superconductor (N/F-QD-S), in which the interplay between the Kondo resonance and the Andreev bound states (ABSs) has not been clearly clarified yet. Here we show that the interference between the Kondo resonance and the ABSs modifies seriously the lineshape of the Kondo resonance, which manifests as a Fano resonance. The ferromagnetic lead with spin-polarization induces an effective field, which leads to splitting both of the Kondo resonance and the ABSs. The spin-polarization together with the magnetic field applied provides an alternative way to tune the lineshape of the Kondo resonances, which is dependent of the relative positions of the Kondo resonance and the ABSs. These results indicate that the interplay between the Kondo resonance and the ABSs can significantly affect the Andreev transport, which could be tested by experiments.
For a normal-quantum dot-superconductor (N-QD-S) device, the microscopic mechanism of Kondo screening is still under the debates. It is found that the spin-induced Yu-Shiba-Rusinov (YSR) bound state possesses effective local moment. The YSR bound state evolves into the Andreev bound states (ABSs) in the presence of normal lead, which are significantly broadened by increasing the coupling. The Kondo resonance observed in Andreev transport can be recognized as the screening of ABSs by the normal lead. Different from the Kondo effect of magnetic impurity in metal, the spin-flipping tunneling through the ABSs level must be associated with the Andreev reflection process.
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