Superconducting Quantum Interference at the Atomic Scale

S. Karan; H. Huang; C. Padurariu; B. Kubala; A. Theiler; A. Black-Schaffer; G. Morrás; A. Levy Yeyati; J. C. Cuevas; J. Ankerhold; K. Kern; C. R. Ast

doi:10.1038/s41567-022-01644-6

arXiv · 2102.12521

Superconducting Quantum Interference at the Atomic Scale

S. Karan·H. Huang·C. Padurariu·B. Kubala·A. Theiler·A. Black-Schaffer·G. Morrás·A. Levy Yeyati·J. C. Cuevas·J. Ankerhold·K. Kern·C. R. Ast

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Abstract

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.

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S. Karan, H. Huang, C. Padurariu, B. Kubala, A. Theiler, A. Black-Schaffer, G. Morrás, A. Levy Yeyati, J. C. Cuevas, J. Ankerhold, K. Kern, C. R. Ast. 2021-02-24. Superconducting Quantum Interference at the Atomic Scale. https://doi.org/10.1038/s41567-022-01644-6

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