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

Joost Ridderbos, Matthias Brauns, Folkert K. De Vries, Jie Shen, Ang Li, Sebastian Kölling, Marcel A. Verheijen, Alexander Brinkman, Wilfred G. Van Der Wiel, Erik P. A. M. Bakkers, Floris A. Zwanenburg*

*Corresponding author for this work

    Research output: Contribution to journalArticleAcademicpeer-review

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    Abstract

    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.
    Original languageEnglish
    Pages (from-to)122-130
    Number of pages9
    JournalNano letters
    Volume20
    Issue number1
    Early online date26 Nov 2019
    DOIs
    Publication statusPublished - 8 Jan 2020

    Keywords

    • UT-Hybrid-D
    • Superconductor−semiconductor hybrid device

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