Regensburg 2025 – scientific programme

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TT: Fachverband Tiefe Temperaturen

TT 32: Superconductivity: Yu-Shiba-Rusinov and Andreev Physics

TT 32.6: Talk

Wednesday, March 19, 2025, 16:15–16:30, H32

Nonequilibrium Josephson and Andreev Transport in Quantum Dot Junctions — •Jordi Picó-Cortés¹, Gloria Platero², Andrea Donarini¹, and Milena Grifoni¹ — ¹Institute for Theoretical Physics, University of Regensburg, 93040 Regensburg, Germany — ²Instituto de Ciencia de Materiales de Madrid (CSIC) 28049 Madrid, Spain

We investigate nonequilibrium transport through superconducting nanojunctions using a Liouville space approach [1]. The formalism allows us to study finite-gap effects, and to account for both quasiparticle and Cooper-pair tunneling. With focus on the weak-tunneling limit, we study the stationary dc and ac current up to second order (cotunneling) in the hybridization energy. For the particular case of a strongly interacting quantum dot sandwiched between two superconductors, we identify the characteristic virtual processes that yield the Andreev and Josephson current and obtain the dependence on the gate and bias voltage for the dc current, the critical current, and the phase-dependent dissipative current. In particular, the critical current is characterized by regions in the stability diagram in which its sign changes from positive to negative, resulting in a multitude of 0−π transitions. The latter signal the interplay between strong interactions and tunneling at finite bias.

[1] J. Picó-Cortés, G. Platero, A. Donarini, M. Grifoni, Phys. Rev. B 110, 125418 (2024).

Keywords: Quantum transport; Coulomb blockade; Josephson junction; Quantum dots; Andreev physics