Parity-Affected Supercurrents in Hybrid Nanorings

•Sergei Sharov1 und Andrei Zaikin2
1Institut für Theoretische Festkörperphysik, Universität Karlsruhe, 76128 Karlsruhe, Germany
2Forschungszentrum Karlsruhe, Institut für Nanotechnologie, 76021, Karlsruhe, Germany

It has been established both experimentally and theoretically that thermodynamic properties of small isolated superconducting islands and grains may strongly depend on the electron parity number. In the present work we investigate the influence of the parity effect on supercurrents in isolated superconducting nanorings interrupted by a quantum point contact(QPC) and threaded by the Aharonov-Bohm magnetic flux.

In order to evaluate superurrents in rings with even and odd total number of electrons we employ the parity projected partition function formalism. Our main results and observations are as follows: (a) the dependence of the supercurrent on the external flux and temperature in both even and odd canonical ensembles derived here may strongly deviate from that established for the grand canonical ensemble, (b) at sufficiently low temperatures supercurrents in rings with odd number of electrons are totally blocked provided QPC has only one conducting mode and (c) this blocking effect gets partially lifted in structures with several or many conducting modes. We also discuss possible realizations of the above effects and demonstrate that our predictions can be directly tested in modern experiments.