Kondo screening in unconventional superconductors: The role of anomalous propagators

TL;DR

This paper emphasizes the importance of anomalous propagators in understanding the Kondo effect in unconventional superconductors, challenging previous interpretations that ignored these propagators and clarifying the correct physical picture.

Contribution

It clarifies that anomalous propagators are crucial for accurately describing Kondo screening in certain superconductors, correcting prior misinterpretations of numerical results.

Findings

Anomalous propagators are essential in Kondo effect analysis in d-wave superconductors.

Previous interpretations of numerical results as two-channel Kondo physics are incorrect.

The treatment ignoring anomalous propagators is exact only in specific cases.

Abstract

The Kondo effect in superconductors is frequently investigated using the local quasiparticle density of states as sole bath characteristics, i.e., the presence of anomalous propagators is ignored. Here we point out that this treatment is exact for a number of situations, including point-like impurities in d-wave superconductors. We comment on recent investigations [M. Matsumoto and M. Koga, J. Phys. Soc. Jpn. 70, 2860 (2001), cond-mat/0011256, and Phys. Rev. B 65, 024508 (2002), cond-mat/0103053] which reached different conclusions: while their numerical results are likely correct, their interpretation in terms of two-channel Kondo physics and an "orbital effect of Cooper pairs" is incorrect.