Superconducting Quantum Interference at the Atomic Scale

• Published in: arXiv.org
• Main Authors: Karan, S, Huang, H, Padurariu, C, Kubala, B, Theiler, A, Black-Schaffer, A, Morrás, G, A Levy Yeyati, Cuevas, J C, Ankerhold, J, Kern, K, Ast, C R
• Format: Paper Journal Article
• Language: English
• Published: Ithaca Cornell University Library, arXiv.org 26.04.2022
• Subjects: Critical current (superconductivity); Interference; Josephson junctions; Phase transitions; Physics - Mesoscale and Nanoscale Physics; Physics - Superconductivity; Quantum computing; Scanning tunneling microscopy; Superconducting quantum interference devices; Superconductivity; Tunnel junctions
• ISSN: 2331-8422
• DOI: 10.48550/arxiv.2102.12521

A single spin in a Josephson junction can reverse the flow of the supercurrent. At mesoscopic length scales, such \(\pi\)-junctions are employed in various instances from finding the pairing symmetry to quantum computing. In Yu-Shiba-Rusinov (YSR) states, the atomic scale counterpart of a single spin in a superconducting tunnel junction, the supercurrent reversal so far has remained elusive. Using scanning tunneling microscopy (STM), we demonstrate such a 0 to \(\pi\) transition of a Josephson junction through a YSR state as we continuously change the impurity-superconductor coupling. We detect the sign change in the critical current by exploiting a second transport channel as reference in analogy to a superconducting quantum interference device (SQUID), which provides the STM with the required phase sensitivity. The measured change in the Josephson current is a signature of the quantum phase transition and allows its characterization with unprecedented resolution.