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Non-Topological Edge-Localized Yu-Shiba-Rusinov States in CrBr3/NbSe2 Heterostructures
by Jan P. Cuperus, Daniel Vanmaekelbergh, Ingmar Swart
Submission summary
| Authors (as registered SciPost users): | Ingmar Swart |
| Submission information | |
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| Preprint Link: | scipost_202503_00058v1 (pdf) |
| Data repository: | https://public.yoda.uu.nl/science/UU01/LB70QM.html |
| Date submitted: | 2025-03-28 09:34 |
| Submitted by: | Swart, Ingmar |
| Submitted to: | SciPost Physics |
| Ontological classification | |
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| Academic field: | Physics |
| Specialties: |
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| Approach: | Experimental |
Abstract
Topological superconductivity is predicted to emerge in certain magnet-superconductor hybrid systems. Here, we revisit the heterostructure of insulating monolayer CrBr3 and NbSe2, for which different conclusions on the presence of topological superconductivity have been reported. Using low-temperature scanning tunneling microscopy and (shot noise) spectroscopy, we find that the superconducting gap well inside the CrBr3 islands is not affected by magnetism. At the island edges, we observe Yu-Shiba-Rusinov (YSR) states at a variety of in-gap positions, including zero energy. The absence of topological superconductivity is verified by extensive dI/dV measurements at the CrBr3 island edges. Our results ask for a more detailed understanding of the interaction between magnetic insulators and superconductors.
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Author comments upon resubmission
Thank you for sharing the referee reports with us and allowing us to resubmit a revised version.
We thank the reviewers for their careful reading of our manuscript and were happy to read their positive feedback. Below we address the few points raised, and list the changes made to the manuscript. We hope that these changes adequately address the comments of the referees.
Best regards from Utrecht,
On behalf of all authors,
Ingmar Swart
List of changes
Referee 1 (report 2)
1. Given the importance of the atomic and electronic structure of the island edges, Fig. 3b would benefit from a larger presentation.
Reply: We agree with the referee that Fig. 3b, in the original manuscript, was quite small. In the revised version, it has been enlarged. To achieve this, the panels of Fig. 3 have been slightly reordered.
2. Is there any spectroscopic indication of the enhanced DoS of the Cr 3d states at the edges?
Reply: The observation of an enhanced DoS at the edges would strengthen our suggestion of the origin of the edge-localized YSR states. Unfortunately, instabilities of the tip-sample junction complicated the spectroscopic characterization of the edges at higher biases. As such, we cannot presently make definitive statements about the Cr 3d DoS at the edges.
Referee 2 (report 3)
1. It can be nice adding a short discussion about the potential role of strain or different twist angle for the absence of bulk Yu-Shiba-Rusinov states.
Reply: We agree with the referee that the role of strain and twist angle should be investigated in more detail. On page 5, line nr. 131, our original manuscript hinted at this via the sentence: “The moiré pattern is not exactly aligned with the rows of Br atoms, showing that the twist angle is not exactly 30° (as suggested in previous reports), but more close to 32°.”
We have modified the final paragraph of the Conclusion to include a brief discussion on this: “The difference may be caused by a different substrate-epilayer interaction (e.g., induced by strain) or, possibly, the presence of defects/impurities. Furthermore, here we found a twist angle of 32°, whereas an angle of 30° was reported previously. A different twist angle may affect the coupling between the ferromagnet and the superconductor.”
Referee 3 (report 1)
Did not recommend/ask for any modifications.
Other changes:
Since the submission of the manuscript, we have revised the method to extract uncertainties in the effective charge from shot-noise measurements. This revised method results in smaller uncertainties. We reanalyzed the shot noise data using the updated method (calculating the uncertainties from the uncertainty in the measured power spectral density directly) and updated Figure 6b and 6c, and the accompanying discussion. The outcome remains unchanged: the updated value of Qeff inside the gap is 1.67 +/- 0.02 e (was 1.7 +/- 0.1 e).