Hard Superconducting Gap and Diffusion-Induced Superconductors in Ge-Si Nanowires

Hard Superconducting Gap and Diffusion-Induced Superconductors in Ge-Si Nanowires

Ridderbos, Joost (University of Twente)
Braun, M. (TU Delft QuTech; Kavli institute of nanoscience Delft)
de Vries, F.K. (University of Twente)
Shen, J. (TU Delft QRD/Kouwenhoven Lab; Kavli institute of nanoscience Delft)
Li, Ang (Eindhoven University of Technology)
Kölling, S. (Eindhoven University of Technology)
Verheijen, Marcel A. (Eindhoven University of Technology)
Brinkman, Alexander (University of Twente)
van der Wiel, Wilfred G. (University of Twente)
Bakkers, E.P.A.M. (Eindhoven University of Technology)
Zwanenburg, Floris A. (University of Twente)

2020

We show a hard superconducting gap in a Ge-Si nanowire Josephson transistor up to in-plane magnetic fields of 250 mT, an important step toward creating and detecting Majorana zero modes in this system. A hard gap requires a highly homogeneous tunneling heterointerface between the superconducting contacts and the semiconducting nanowire. This is realized by annealing devices at 180 °C during which aluminum interdiffuses and replaces the germanium in a section of the nanowire. Next to Al, we find a superconductor with lower critical temperature (TC = 0.9 K) and a higher critical field (BC = 0.9-1.2 T). We can therefore selectively switch either superconductor to the normal state by tuning the temperature and the magnetic field and observe that the additional superconductor induces a proximity supercurrent in the semiconducting part of the nanowire even when the Al is in the normal state. In another device where the diffusion of Al rendered the nanowire completely metallic, a superconductor with a much higher critical temperature (TC = 2.9 K) and critical field (BC = 3.4 T) is found. The small size of these diffusion-induced superconductors inside nanowires may be of special interest for applications requiring high magnetic fields in arbitrary direction.

Ge−Si nanowire
hard superconducting gap
Josephson junction
Majorana quasiparticle
Superconductor−semiconductor hybrid device
topological superconductivity

http://resolver.tudelft.nl/uuid:71e8d032-3990-4d1c-a98e-c96ef417f78b

https://doi.org/10.1021/acs.nanolett.9b03438

1530-6984

Nano Letters: a journal dedicated to nanoscience and nanotechnology, 20 (1), 122-130

Institutional Repository

journal article

© 2020 Joost Ridderbos, M. Braun, F.K. de Vries, J. Shen, Ang Li, S. Kölling, Marcel A. Verheijen, Alexander Brinkman, Wilfred G. van der Wiel, E.P.A.M. Bakkers, Floris A. Zwanenburg