Special Seminar on 6 December 2023 at 2 p.m. in the ÚFKL hall

Alžběta Kadlecová:
Investigating superconducting quantum dots: Influence of coupling asymmetry in the DC setup and the AC Josephson current mystery

A quantum dot attached to BCS superconducting leads, commonly realised e.g. by InAs nanowires or carbon nanotubes, is a tunable system whose physical properties can be experimentally controlled either by the gate voltage or by the superconducting phase difference. As such, it is an interesting building block for potential applications and an excellent laboratory for the physics of superconducting nanostructures.

From the theoretical point of view, the system is described by the single-impurity Anderson model, the solution of which usually requires heavy numerical methods. However, I will demonstrate how to comprehend the influence of asymmetrical dot-lead couplings on transport properties in the phase-biased (DC Josephson) setup using analytical means. The coupling asymmetry and the phase difference can be combined into one function (the symmetry-asymmetry relation). This enables the calculation of the physical properties of a system with coupling asymmetry from the properties of its effective symmetric counterpart. Further, I will show the consequences of coupling asymmetry on the notion of Kondo universality in superconducting quantum dots, and specifically on the 0−π impurity quantum phase transition.

If time permits, I will also touch upon possible interpretations of an AC Josephson current measurement in a carbon nanotube superconducting quantum dot.

[1] A. Kadlecová, M. Žonda, T. Novotný, Phys. Rev. B 95(19), 195114 (2017).
[2] A. Kadlecová, M. Žonda, V. Pokorný, and T. Novotný, Phys. Rev. Applied 11, 044094 (2019).
[3] D. Watfa, R. Delagrange, A. Kadlecová, M. Ferrier, A. Kasumov, H. Bouchiat, and R. Deblock. Phys. Rev. Lett. 126, 126801 (2021).