Tunable superconductivity and engineered current-phase relation in planar Germanium
M. Valentini1, O. Sagi1, T. de Gijsel1, K. Aggarwal1, L. Baghumyan1, M. Janik1, J. Jung2, M. Verheijen2, S. Calcaterra3, A. Ballabio2, D. Chrastina3, E.P.A.M. Bakkers2, G. Isella2 and G. Katsarsos1
1 Institute of Science and Technology Austria
2 Eindhoven University of Technology
3 Politecnico di Milano
III-V materials, like InAs and InSb, are the leading platforms for the realization of gatemons and for the quest of Majorana zero modes. Here we investigate Germanium as an alternative platform [1]. In the past years, dramatic progress has been made in inducing superconductivity in planar Germanium either by enhancing the proximity effect using a double layer of superconductors [2] or by creating a low-disorder interface between the germanium hole gas and an annealed germanosilicide superconductor [3]. Here, we show that we can reliably induce superconductivity in a Germanium hole gas by evaporating aluminum on top of a thin Si0.3Ge0.7 spacer which separates the superconductor from the quantum well. We estimate transparencies close to unity and we reveal a superconducting hard gap which can be tuned by the Si0.3Ge0.7 spacer. Finally, we show the exchange of pairs of Cooper pairs between two superconducting leads, highlighting the potential of Germanium quantum well as protected qubit [4].
[1] G. Scappucci et al., Nature Reviews Materials 6.10 (2021): 926-943.
[2] K. Aggarwal et al., Physical Review Research 3.2 (2021): L022005.
[3] A. Tosato et al., arXiv:2206.00569 (2022).
[4] C. Schrade, et al., PRX Quantum 3.3 (2022): 030303.