Superconductors with a Topological Gap
Round 1
Reviewer 1 Report
The manuscript titled “Superconductors with Topological Gap” by Marai Cristina Diamantini submitted to Condensed Matter Journal to be published in the
special issue proposes a superconductivity mechanism where the order of the ground state is of topological origin. Dr. Diamantini proposes a low-energy effective theory formulated in terms of emerging gauge fields. This mechanism considers the emergence of this superconductivity mechanism in Josephson junction arrays and in thin films where the thickness is of the same order as the the superconducting coherence length. It is of particular interest the discussion of granular superconductivity near a metal-insulator transition in 2+1 dimension where superconductivity emerges from the global condensation of the droplet charges in a phase with no vortices where the droplets are connected by quantum tunnelling, forming global phase coherence in a global condensate. In this phase tunnelling percolation on the droplets forms a global condensate as it has been experimentally observed in high temperature superconductors (Campi et al. Condensed Matter, 2021, 6(4), 40) therefore the author could site experimental evidence for heterogeneous granular high temperature superconductors supporting her proposed scenario published. Moreover experimental realization of artificial superlattice of quantum wells with tunnelling between superconducting units where the separation is of the order of coherence length has been discussed by (Mazziotti et al J. Applied Physics, 132, 193908, 2022) and could be cited in this review to attract a widere audience.
In summary the new physics discussed by Diamantini paper point out relevance of advances in the role of topology in quantum complex matter and it is suitabke of publication in condensed matter with minor changes
Author Response
I thank Referee 1 for her/his very positive comments and for pointing out two relevant references that I have included in the manuscript.
Reviewer 2 Report
The paper "Superconductors with topological gap" reviews the emergence of superconducting states in systems not described by the Landau theory of quantum phase transitions. The author demonstrate that non-trivial superconducting states can have topological origin with its low-energy excitations being described, e.g., by Chern-Simons field theory. The paper is concise, well written (only minor typos), and of course influenced by original works published by author herself. Because of that, I recommend its publication as a review in Condensed Matter.
Author Response
I thank Referee 2 for her/his very positive comments.
Reviewer 3 Report
The submitted Manuscript concerns unusual effects that might occur in the superconducting systems at certain conditions, for example,in the case of a finite sample size. I appreciate the general quality of the presentation, but I sincerely cannot follow the overall meaning of the story. Too many very different approaches and things are mentioned, at the same time it is difficult to find a single one that would be taken to the meaningfully formulated final results.Throughout the manuscript, the considered effects are presented as strongly opposing the usual well-accepted (and generally working well) theory of superconductivity. Yet, I feel that they may be considered as some small additions to the existing and thoroughly tested theory. An example can be found in the abstract: the Josefson effect is much rather a small addition on top of the already present superconducting phase, then something completely different.
For this reason I apologize, but I cannot recommend the manuscript for publication. One the general level I can understand that we need to be in constant search for new interesting effects occurring alongside with superconductivity, however, I find the presented results rather unclear.
Author Response
Referee 3: I do not understand the comments of Referee 3. She/he writes:”The submitted
Manuscript concerns unusual e↵ects that might occur in the superconducting systems at cer- tain conditions, for example,in the case of a finite sample size....Throughout the manuscript, the considered e↵ects are presented as strongly opposing the usual well-accepted (and gen- erally working well) theory of superconductivity.” . Since we are talking about (2+1)- dimensional systems this comment dosen’t make any sense because, in case of infinite size samples, the standard mechanism of superconductivity based on the Anderson-Higgs mech- anism cannot be applied at any temperature di↵erent from T=0 because of Mermim-Wagner theorem. The Referee seems to be not aware that what she/he calls standard theory can be used for all reasonable sample sizes used in experiments since this e↵ect can be neglected. So if she/he is looking for a mechanism that works both for finite and infinite size sample this CANNOT BE the standard superconductivity mechanism. Moreover, the Referee seems not to understand that in order to explain the experimentally observed superconductivity in the granular films it’s no possible to advocate the Anderson-Higgs mechanism since the Pearl length screening the vortex interactions is typically larger than the sample size. A new mechanism is thus necessary.
The Referee also writes: ”Too many very di↵erent approaches and things are mentioned, at the same time it is dicult to find a single one that would be taken to the meaningfully formulated final results.” . In the manuscript there is only one appoch, the topological mass mechanism. Since this mechanism is valid in any space-time dimensions, I presented it, first, in a general way using the standard forms language. Maybe the Referee is not familiar with it.
The Referee feels that: ”Yet, I feel that they (my models) may be considered as some small additions to the existing and thoroughly tested theory. An example can be found in the abstract: the Josefson e↵ect is much rather a small addition on top of the already present superconducting phase, then something completely di↵erent.” I do not understand this comments at all. Josephson junction arrays are the paradigmatic example of a granular materials (although engineered) and they are described by a topological gauge theory, as is well known.
