Superconductor-Semiconductor Devices with 2D Holes in Germanium*

The coupling of superconductors to semiconductors receives widespread interest due to their potential for realizing topological superconductivity, interferometers and Andreev Bound State devices [1, 2]. The quality of the induced gap, heavily influenced by the transparency of the superconductor-semiconductor interface, presents a crucial challenge for realizing such devices.
Here, we study proximity induced superconductivity in germanium quantum wells coupled to aluminium. The presence of strong spin-orbit interaction, tunable g-factor and high mobility make germanium an attractive semiconducting platform. Combined with the ease of ohmic contact formation due to Fermi level pinning, Ge-Al is a promising material system for hybrid semiconductor-superconductor devices. We achieved transparencies of 65% and I_CR_N products of up to 50µV, about three times higher than previously reported [3, 4].
[1] R. M. Lutchyn et al., Phys. Rev. Lett. 105, 077001 (2010).
[2] J.-D. Pillet et al., Nature Physics 6, 965 (2010).
[3] N. W. Hendrickx et al., Phys. Rev. B 99, 075435 (2019)
[4] F. Vigneau et al., Nano Lett. 19, 1023-1027 (2019)