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

0467075 - FZÚ 2017 RIV DE eng J - Journal Article
Janiš, Václav - Pokorný, Vladislav - Žonda, M.
Spin-symmetric solution of an interacting quantum dot attached to superconducting leads: Andreev states and the 0-pi transition.
European Physical Journal B. Roč. 89, č. 9 (2016), 1-12, č. článku 197. ISSN 1434-6028. E-ISSN 1434-6036
R&D Projects: GA ČR GA15-14259S
Institutional support: RVO:68378271
Keywords : mesoscopic and nanoscale systems * Andreev bound states * 0-pi transition * perturbation theory
Subject RIV: BM - Solid Matter Physics ; Magnetism
Impact factor: 1.436, year: 2016

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-pi transition. We show that the spin-symmetric solution becomes degenerate beyond this interaction, in the pi 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.
Permanent Link: http://hdl.handle.net/11104/0265216