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Unconventional Superconductivity arising from Multipolar Kondo Interactions

by Adarsh S. Patri, Yong Baek Kim

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Submission summary

Authors (as registered SciPost users): Adarsh Patri
Submission information
Preprint Link: scipost_202104_00029v2  (pdf)
Date submitted: 2021-07-16 21:07
Submitted by: Patri, Adarsh
Submitted to: SciPost Physics
Ontological classification
Academic field: Physics
Specialties:
  • Condensed Matter Physics - Theory
Approach: Theoretical

Abstract

The nature of unconventional superconductivity is intimately linked to the microscopic nature of the pairing interactions. In this work, motivated by cubic heavy fermion compounds with embedded multipolar moments, we theoretically investigate superconducting instabilities instigated by multipolar Kondo interactions. Employing multipolar fluctuations (mediated by RKKY interaction) coupled to conduction electrons via two-channel Kondo and novel multipolar Kondo interactions, we uncover a variety of superconducting states characterized by higher-angular momentum Cooper pairs, J=0,1,2,3. We demonstrate that both odd and even parity pairing functions are possible, regardless of the total angular momentum of the Cooper pairs, which can be traced back to the atypical nature of the multipolar Kondo interaction that intertwines conduction electron spin and orbital degrees of freedom. We determine that different (point-group) irrep classified pairing functions may coexist with each other, with some of them characterized by gapped and point node structures in their corresponding quasiparticle spectra. This work lays the foundation for discovery and classification of superconducting states in rare-earth metallic compounds with multipolar local moments.

Author comments upon resubmission

Dear Editor,

Thank you for the insightful questions regarding our manuscript.
We have answered all the questions and implemented the changes recommended by referees in our revised manuscript.
We have attached a detailed reply to the report (PDF format) under the author reply to the referee for convenience.

Thank you.

List of changes

The specific additions to the manuscript are (also detailed in the PDF of the author reply to the referee):
- Described the physical reasoning behind the choices of the phenomenological parameters (in Appendix H).
- Included a revised caption and labelled subfigures in Fig. 4 for clarity.
- Described the time-reversal properties of the realized superconducting states from both two-channel and novel Kondo interactions.
- Provided the momentum-space distribution of the various order parameters (to make connections with conventional discussions of superconductivity) in a newly constructed Appendix I.
- Corrected stylistic errors in the References.
- Clarified and confirmed the anti-symmetrization of the Cooper pair operators.

The additions are indicated in blue font in the revised manuscript for convenience.

Current status:
Has been resubmitted

Reports on this Submission

Report #2 by Anonymous (Referee 2) on 2021-8-17 (Invited Report)

  • Cite as: Anonymous, Report on arXiv:scipost_202104_00029v2, delivered 2021-08-17, doi: 10.21468/SciPost.Report.3404

Report

I am still not satisfied by the author’s explanation of the “mixing” of order parameters in different irreps. I undestand that their Hamiltonian does not break symmetry. However, if converted to LG notation, their Hamiltonian states that OP1 couples to the *spatial gradient* of OP2 with the appropriate symmetry (and vice versa), since the scattering vertex is q dependent and symmetry breaking. This is not the same as mixing irreps, which would be q-independent. It does not mean that once OP1 exists, OP2 also exists, which is the common meaning of mixing/coexisting OPs. I assume this coupling, which always exists in a LG expansion, has a particularly large coefficient due to the unusual Kondo interaction, and so this spatial gradient is likely to be substantially present? Their language here is misleading and should be corrected.

I am also concerned by their derivation of this q-dependent interaction vertex. Typically, if I write down a pairing interaction with f(q = k-k’) = cos qx - cos qy, then I separate it into even/odd parity components with f(k-k’) +/- f(k+k’) and then separate these to write f(k) f(k’), where then the d-wave symmetry of f(q) is actually split between the two superconducting order parameters, as opposed to keeping it with the interaction vertex, as they do here. Now, given the symmetry of the Gamma’s involved, they may be correct to do what they have done, however, it is at all not obvious. Given that what they are doing is so unusual, they must explain why their choice is the correct one, in detail, particularly why the momentum dependence is being kept with the vertex rather than going with the superconducting order parameter.

These are serious concerns, and I cannot support publication until they are addressed.

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Author:  Adarsh Patri  on 2021-10-29  [id 1888]

(in reply to Report 2 on 2021-08-17)
Category:
answer to question

Dear Referee,

We thank you for your insightful questions, and we attach a PDF document answering your questions.
We have also incorporated the respective changes in the revised manuscript.

Sincerely,
Adarsh S. Patri, Yong Baek Kim

Attachment:

ref_report_sc_multipolar_2.pdf

Report #1 by Anonymous (Referee 3) on 2021-7-22 (Invited Report)

Report

The authors answer all the comments properly and the revised manuscript is easier to follow. Thus, I believe the paper is now suitable for publication.

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  • significance: -
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