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

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• 作者：Václav Janiš ; Vladislav Pokorný ; Martin Žonda
• 关键词：Mesoscopic and Nanoscale Systems
• 刊名：The European Physical Journal B - Condensed Matter
• 出版年：2016
• 出版时间：September 2016
• 年：2016
• 卷：89
• 期：9
• 全文大小：497 KB
• 刊物类别：Physics and Astronomy
• 刊物主题：Physics
  Condensed Matter
  Physics
  Complexity
  Fluids
  Solid State Physics and Spectroscopy
  Superconductivity, Superfluidity and Quantum Fluids
  
• 出版者：Springer Berlin / Heidelberg
• ISSN：1434-6036
• 卷排序：89

文摘

Behavior of Andreev gap states in a quantum dot with Coulomb repulsion symmetricallyattached to superconducting leads is studied via the perturbation expansion in theinteraction strength. We find the exact asymptotic form of the spin-symmetric solution forthe Andreev states continuously approaching the Fermi level. We thereby derive a criticalinteraction 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-symmetricsolution becomes degenerate beyond this interaction, in the π phase, and the Andreevstates do not split unless the degeneracy is lifted. We further demonstrate that thedegeneracy of the spin-symmetric state extends also into the 0 phase in which the solutions with zero andnon-zero frequencies of the Andreev states may coexist.