• Open Access

Zeeman effects on Yu-Shiba-Rusinov states

T. Machida, Y. Nagai, and T. Hanaguri
Phys. Rev. Research 4, 033182 – Published 6 September 2022

Abstract

When the exchange interaction between the impurity spin and the spins of itinerant quasiparticles is strong or weak enough, the ground states for a magnetic impurity in a superconductor are the screened or free spins, respectively. In both cases, the lowest excited state is a bound state within the superconducting gap, known as the Yu-Shiba-Rusinov (YSR) state. The YSR state is spatially localized, energetically isolated, and fully spin polarized, leading to applications such as functional scanning probes. While any application demands identifying whether the impurity spin is screened or free, a suitable experimental technique has been elusive. Here we demonstrate an unambiguous way to determine the impurity ground state using the Zeeman effect. We performed ultralow-temperature scanning tunneling spectroscopy of junctions formed between a Cu(111) surface and superconducting Nb tips decorated by single magnetic Fe atoms. Depending on the condition of the Fe adsorbate, the YSR peak in the spectrum either splits or shifts in a magnetic field, signifying that the Fe spin is screened or free, respectively. Our observations provide renewed insights into the competition between magnetism and superconductivity and constitute a basis for the applications of the YSR state.

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  • Received 25 May 2022
  • Accepted 17 August 2022

DOI:https://doi.org/10.1103/PhysRevResearch.4.033182

Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article's title, journal citation, and DOI.

Published by the American Physical Society

Physics Subject Headings (PhySH)

Condensed Matter, Materials & Applied Physics

Authors & Affiliations

T. Machida1,2,*, Y. Nagai3,4, and T. Hanaguri1

  • 1RIKEN Center for Emergent Matter Science, Wako, Saitama 351-0198, Japan
  • 2Precursory Research for Embryonic Science and Technology, Japan Science and Technology Agency, Tokyo 102-0076, Japan
  • 3CCSE, Japan Atomic Energy Agency, 178-4-4 Wakashiba, Kashiwa, Chiba 277-0871, Japan
  • 4Mathematical Science Team, RIKEN Center for Advanced Intelligence Project, 1-4-1 Nihonbashi, Chuo-ku, Tokyo 103-0027, Japan

  • *Corresponding author: tadashi.machida@riken.jp

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Vol. 4, Iss. 3 — September - November 2022

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