The co-integration of spin, superconducting, and topological systems is emerging as an exciting pathway for scalable and high-fidelity quantum information technology. High-mobility planar germanium is a front-runner semiconductor for building quantum processors with spin-qubits, but progress with hybrid superconductor-semiconductor devices is hindered because obtaining a superconducting gap free of subgap states (hard gap) has proven difficult. Here we solve this challenge by developing a low-disorder, oxide-free interface between high-mobility planar germanium and a germanosilicide parent superconductor. This superconducting contact is formed by the thermally-activated solid phase reaction between a metal (Pt) and the semiconductor heterostructure (Ge/SiGe). Electrical characterization reveals near-unity transparency in Josephson junctions and, importantly, a hard induced superconducting gap in quantum point contacts. Furthermore, we demonstrate phase control of a Josephson junction and study transport in a gated two-dimensional superconductor-semiconductor array towards scalable architectures. These results expand the quantum technology toolbox in germanium and provide new avenues for exploring monolithic superconductor-semiconductor quantum circuits towards scalable quantum information processing.
@article{arxiv.2206.00569,
title = {Hard superconducting gap in germanium},
author = {Alberto Tosato and Vukan Levajac and Ji-Yin Wang and Casper J. Boor and Francesco Borsoi and Marc Botifoll and Carla N. Borja and Sara Martí-Sánchez and Jordi Arbiol and Amir Sammak and Menno Veldhorst and Giordano Scappucci},
journal= {arXiv preprint arXiv:2206.00569},
year = {2023}
}