A single spin in a Josephson junction can reverse the flow of the supercurrent. At mesoscopic length scales, such π-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 π 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.
@article{arxiv.2102.12521,
title = {Superconducting Quantum Interference at the Atomic Scale},
author = {S. Karan and H. Huang and C. Padurariu and B. Kubala and A. Theiler and A. Black-Schaffer and G. Morrás and A. Levy Yeyati and J. C. Cuevas and J. Ankerhold and K. Kern and C. R. Ast},
journal= {arXiv preprint arXiv:2102.12521},
year = {2023}
}
Comments
10 pages, 6 figures, including supplementary information