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  • Open Access

Yu-Shiba-Rusinov states in color-superconducting quark matter

Virgil V. Baran1,2,* and Jens Paaske3

  • *Contact author: virgil.v.baran@unibuc.ro
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Phys. Rev. D 112, 096021 – Published 18 November, 2025

DOI: https://doi.org/10.1103/vmbp-bqvh

Abstract

The high-density region of the QCD phase diagram displays an intricate competition between color superconductivity and the QCD Kondo effect due to color exchange in quark matter containing a single heavy quark impurity. We explore the characteristic impurity-induced superconducting subgap states arising in such systems by generalizing the surrogate model solver, recently considered in the context of condensed matter physics [Phys. Rev. B 108, L220506 (2023)]. The method consists of approximating the full superconducting bulk by only a small number of effective levels whose parameters are chosen so as to best reproduce the Matsubara frequency dependence of the impurity-bulk hybridization function. We numerically solve a surrogate QCD Kondo model describing a quantum impurity color exchange coupled to a two-color two-flavor superconducting bulk. The results directly indicate the presence of multiple phase transitions as the coupling of the impurity to the bulk is increased, due to the interplay between various overscreened states. The methods introduced here are straightforward enough to be extended to more realistic QCD scenarios.

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Phys. Rev. D 112, 096021– Published 18 November, 2025
  • Received 19 July 2025
  • Accepted 27 October 2025
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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. Funded by SCOAP3.

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