Strong nonlocal tuning of the current-phase relation of an Andreev molecule
Mátyás Kocsis1,2, Zoltán Scherübl1,2, Gergő Fülöp1,2, Péter Makk1,3, Szabolcs Csonka1,2
1 Department of Physics, Institute of Physics, Budapest University of Technology and Economics, Műegyetem rkp. 3., H-1111 Budapest, Hungary
2 MTA-BME Superconducting Nanoelectronics Momentum Research Group, Műegyetem rkp. 3., H-1111 Budapest, Hungary
3 MTA-BME Correlated van der Waals Structures Momentum Research Group, Műegyetem rkp. 3., H-1111 Budapest, Hungary
Recent advances in hybrid superconducting – semiconducting structures allows for well-controlled fabrication of complex nanodevices. Placing two Josephson junctions next to each other, closer than the superconducting coherence length, the Andreev bound states hybridize into an Andreev molecular state. Here we investigate the scenario where the Josephson junctions are formed of a quantum dot. Similar molecular states were theoretically investigated in ballistic channels, in the absence of electron-electron interactions, where the non-local tunability of the supercurrent was argued [1-2]. In quantum dots, the presence of the Coulomb interaction and the possibility of electrostatic gating allows for a more versatile tunability. First of all, doublet ground states are only possible with finite Coulomb interactions.
In this contribution we discuss how the molecular state is formed and how the supercurrent of a given junction is affected by the control parameters of the other junction, namely the level position and the superconducting phase difference. Besides the usual parity driven 0-π transition we identified 0 and π regions within the same ground state. We demonstrate a large, strongly tunable φ0 phase in the absence of spin-orbit interaction. Furthermore exotic current phase relations and superconducting diode effect are discussed. The non-local tunability of these effects are the smoking gun features of the Andreev molecular state. This work opens the way of a better understading of complex hybrid devices.
[1] J.-D. Pillet, V. Benzoni, J. Griesmar, J.-L. Smirr, and Ç. Ö. Girit, Nano Letters 19, 7138 (2019)
[2] . J.-D. Pillet, V. Benzoni, J. Griesmar, J.-L. Smirr, Ç. Ö. Girit, SciPost Phys. Core 2, 009 (2020)