Spin-symmetric solution of an interacting quantum dot attached to superconducting leads: Andreev states and the 0-π transition

Václav Janiš (), Vladislav Pokorný and Martin Žonda
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Václav Janiš: Institute of Physics, The Czech Academy of Sciences, Na Slovance 2
Vladislav Pokorný: Institute of Physics, The Czech Academy of Sciences, Na Slovance 2
Martin Žonda: Faculty of Mathematics and Physics, Charles University in Prague, Ke Karlovu 5

The European Physical Journal B: Condensed Matter and Complex Systems, 2016, vol. 89, issue 9, 1-12

Abstract: Abstract Behavior of Andreev gap states in a quantum dot with Coulomb repulsion symmetrically attached to superconducting leads is studied via the perturbation expansion in the interaction strength. We find the exact asymptotic form of the spin-symmetric solution for the Andreev states continuously approaching the Fermi level. We thereby derive a critical interaction at which the Andreev states at zero temperature merge at the Fermi energy, being the upper bound for the 0-π transition. We show that the spin-symmetric solution becomes degenerate beyond this interaction, in the π phase, and the Andreev states do not split unless the degeneracy is lifted. We further demonstrate that the degeneracy of the spin-symmetric state extends also into the 0 phase in which the solutions with zero and non-zero frequencies of the Andreev states may coexist.

Keywords: Mesoscopic; and; Nanoscale; Systems (search for similar items in EconPapers)
Date: 2016
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DOI: 10.1140/epjb/e2016-70299-7

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