Current-Phase Relation of Hybrid Semiconductor-Superconductor Gatemon Devices
H. Zheng1, T. Jenniskens1,2, R. Haller1, J. Ridderbos4, A. Kononov1, E. Bakkers2, A. Baumgartner1,3, C. Schönenberger1,3
1 Dep. of Physics, University of Basel, Klingelbergstr. 82, 4056 Basel, Switzerland
2 Dep. of Appl. Phys., Eindhoven University of Technology, Eindhoven, The Netherlands
3 Swiss Nanoscience Institute, University of Basel, Klingelbergstr. 82, Basel, Switzerland
4 MESA Institute for Nanotechnology, University of Twente, Enschede, The Netherlands
The current-phase relationship (CPR) [1], as one of the most fundamental properties of a Josephson junction, contains information about the Andreev bound state (ABS) spectrum in weak links and can serve as a powerful tool to explore physical phenomena like π-junction physics due to electron-electron interactions [2], 4π-periodicity due to topology [3] and other phase-effects caused by spin-orbit interaction combined with magnetic Zeeman fields.[4]
Here we report CPR measurements for Josephson junctions based on Ge/Si core/shell nanowires, embedded in a superconducting quantum interference device (SQUID) geometry. The Josephson junctions are fabricated by annealing Al into the Ge core.[5] With electrical side gates, we individually tuned the critical current in each arm. In an asymmetrical supercurrent configuration, we find a non-reciprocal critical current when changing the current bias direction, often described as the Josephson diode effect. This effect can be understood as caused by the non-sinusoidal CPR of a highly transmissive junction together with an applied flux bias that leads to an effective non-reciprocal critical current.[6] Most intriguingly, we find an anomalous CPR with a dominant cos(2φ) dependence for selected gate voltages, an effect we currently investigate in more detail.
If time permits, we will report on similar results in another material platform, in hybrid devices fabricated in a proximitized quantum well structure.
We acknowledge funding from the EC, the Swiss NSF, the SNI and fruitful collaborations with the TU-Twente, TU-Eindhoven, the Qdev team at Niels-Bohr Copenhagen and inspiring discussions with G. Katsaros and A. Levy-Yeyati.
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[2] S. De Franceschi, L. Kouwenhoven, C. Schönenberger, W. Wernsdorfer, Hybrid superconductor-quantum dot devices, Nature Phys. 5, 703 (2010).
[3] R. M. Lutchyn, J. D. Sau, and S. Das Sarma, Majorana Fermions and a Topological Phase Transition in Semiconductor-Superconductor Heterostructures, Phys. Rev. Lett. 105, 077001 (2010).
[4] D. B. Szombati, S. Nadj-Perge, D. Car, S. R. Plissard, E. P. A. M. Bakkers, and L. P. Kouwenhoven, Josephson Φ0-Junction in Nanowire Quantum Dots, Nature Phys 12, 568 (2016).
[5] J. Ridderbos et al., Hard Superconducting Gap and Diffusion-Induced Superconductors in Ge–Si Nanowires, Nano Lett. 20, 122 (2020).
[6] R. S. Souto, M. Leijnse, and C. Schrade, The Josephson Diode Effect in Supercurrent Interferometers, Phys. Rev. Lett. 129, 267702 (2022).