Parity-conserving Cooper-pair transport and ideal superconducting diode in planar germanium

• Published in: Nature communications Vol. 15; no. 1; p. 169
• Main Authors: Valentini, Marco, Sagi, Oliver, Baghumyan, Levon, de Gijsel, Thijs, Jung, Jason, Calcaterra, Stefano, Ballabio, Andrea, Aguilera Servin, Juan, Aggarwal, Kushagra, Janik, Marian, Adletzberger, Thomas, Seoane Souto, Rubén, Leijnse, Martin, Danon, Jeroen, Schrade, Constantin, Bakkers, Erik, Chrastina, Daniel, Isella, Giovanni, Katsaros, Georgios
• Format: Journal Article
• Language: English
• Published: London Nature Publishing Group UK 02.01.2024; Nature Publishing Group; Nature Portfolio
• Subjects: 639/766/119/1003; 639/925/927/1064; Aluminum; Condensed Matter Physics; Cooper pairs; Den kondenserade materiens fysik; Electrical junctions; Electrons; Fysik; Germanium; Humanities and Social Sciences; Interference; Josephson junctions; multidisciplinary; Natural Sciences; Naturvetenskap; Physical Sciences; Quantum wells; Qubits (quantum computing); Science; Science (multidisciplinary); Superconducting quantum interference devices; Superconductivity; Technology
• ISSN: 2041-1723; 2041-1723
• DOI: 10.1038/s41467-023-44114-0

Superconductor/semiconductor hybrid devices have attracted increasing interest in the past years. Superconducting electronics aims to complement semiconductor technology, while hybrid architectures are at the forefront of new ideas such as topological superconductivity and protected qubits. In this work, we engineer the induced superconductivity in two-dimensional germanium hole gas by varying the distance between the quantum well and the aluminum. We demonstrate a hard superconducting gap and realize an electrically and flux tunable superconducting diode using a superconducting quantum interference device (SQUID). This allows to tune the current phase relation (CPR), to a regime where single Cooper pair tunneling is suppressed, creating a sin 2 φ CPR. Shapiro experiments complement this interpretation and the microwave drive allows to create a diode with ≈ 100% efficiency. The reported results open up the path towards integration of spin qubit devices, microwave resonators and (protected) superconducting qubits on  the same silicon technology compatible platform. M. Valentini et al. study superconducting quantum interference devices (SQUIDs) where the weak link of the Josephson junctions is a germanium 2D hole gas. They report signatures of the tunneling of pairs of Cooper pairs. For a particular microwave drive power, they observe a 100% efficient superconducting diode effect.