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TT: Fachverband Tiefe Temperaturen

TT 6: Superconductivity: Tunnelling and Josephson Junctions I

TT 6.12: Talk

Monday, March 18, 2024, 12:45–13:00, H 3010

Quantum size effects on Andreev transport in Josephson junctions — Gábor Csire¹, •Balázs Ujfalussy², and Nóra Kucska² — ¹Materials Center Leoben Forschung GmbH, Roseggerstraße 12, 8700 Leoben, Austria — ²HUN-REN Wigner Research Centre for Physics, Budapest, Hungary

Measurements of the critical current density, superconducting coherence length, and superconducting transition temperature in single-domain, epitaxially-grown Nb(110)/Au(111)/Nb(110) junctions show an oscillatory behavior as a function of the thickness of the Au layers. We apply the first principles-based microscopic theory of inhomogeneous relativistic superconductivity to understand both the fundamentals and the specifics of the underlying physical mechanism of this behavior. We study the effects of spin-orbit coupling, and the effect of confinement and show that they induce a complex structure of Andreev states in the superconducting state which in turn modifies the quasi-particle spectrum and the Josephson supercurrent. Our study reveals the coexistence of two superconducting phases in the gold layers, the usual intraband s-wave phase and an additional Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) phase stemming from interband pairing (without magnetic field). The results indicate the rich interplay between quantum size and proximity effects which suggests the possibility of modifying superconducting transport properties by exploiting thickness-dependent quantum size effects.

Keywords: quantum confinement; spin-orbit coupling; interband pairing; Andreev states; FFLO phase