Granular aluminum induced superconductivity in germanium for hole spin-based hybrid devices

Giorgio Fabris; Paul Falthansl-Scheinecker; Devashish Shah; Daniel Michel Pino; Maksim Borovkov; Anton Bubis; Kevin Roux; Dina Sokolova; Alejandro Andres Juanes; Tommaso Costanzo; Inas Taha; Aziz Genç; Jordi Arbiol; Stefano Calcaterra; Afonso De Cerdeira Oliveira; Daniel Chrastina; Giovanni Isella; Ruben Seoane Souto; Maria Jose Calderon; Ramon Aguado; Jose Carlos Abadillo-Uriel; Georgios Katsaros

arXiv · 2602.21364

Granular aluminum induced superconductivity in germanium for hole spin-based hybrid devices

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Abstract

In superconductor-semiconductor hybrid structures, superconductivity and spin polarization are competing effects as magnetic fields break Cooper pairs. They can be combined using thin films and in-plane magnetic fields, an approach that enabled the pursuit of Majorana zero modes, Kitaev chains, and Andreev spin qubits (ASQs), but remains challenging for materials with small in-plane $g$-factors or when out-of-plane fields are required. We demonstrate that granular aluminium (grAl), composed of nanometre-scale aluminium grains embedded in an amorphous oxide matrix, can overcome this limitation. By depositing grAl on Ge/SiGe heterostructures, we induce a hard superconducting gap with BCS peaks at $305~\mu\mathrm{eV}$ and magnetic-field resilience for both the in-plane and out-of-plane directions, allowing Zeeman splitting of Yu-Shiba-Rusinov (YSR) states beyond $50~\mu\mathrm{eV}$ (12 GHz). Leveraging this robustness, we reveal signatures of hole physics and discuss a driving mechanism for ASQs regardless of the strength of the Rashba spin-orbit coupling in planar germanium.

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Giorgio Fabris, Paul Falthansl-Scheinecker, Devashish Shah, Daniel Michel Pino, Maksim Borovkov, Anton Bubis, Kevin Roux, Dina Sokolova, Alejandro Andres Juanes, Tommaso Costanzo, Inas Taha, Aziz Genç, Jordi Arbiol, Stefano Calcaterra, Afonso De Cerdeira Oliveira, Daniel Chrastina, Giovanni Isella, Ruben Seoane Souto, Maria Jose Calderon, Ramon Aguado, Jose Carlos Abadillo-Uriel, Georgios Katsaros. 2026-02-24. Granular aluminum induced superconductivity in germanium for hole spin-based hybrid devices. https://arxiv.org/abs/2602.21364

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