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Evidence of $φ$0-Josephson junction from skewed diffraction patterns in Sn-InSb nanowires
by B. Zhang, Z. Li, V. Aguilar, P. Zhang, M. Pendharkar, C. Dempsey, J. S. Lee, S. D. Harrington, S. Tan, J. S. Meyer, M. Houzet, C. J. Palmstrom, S. M. Frolov
Submission summary
| Authors (as registered SciPost users): | Sergey Frolov · Bomin Zhang · Po Zhang |
| Submission information | |
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| Preprint Link: | https://arxiv.org/abs/2212.00199v5 (pdf) |
| Code repository: | https://zenodo.org/records/7374094 |
| Data repository: | https://zenodo.org/records/7374094 |
| Date submitted: | 2024-09-27 03:50 |
| Submitted by: | Zhang, Bomin |
| Submitted to: | SciPost Physics |
| Ontological classification | |
|---|---|
| Academic field: | Physics |
| Specialties: |
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| Approaches: | Theoretical, Experimental, Phenomenological |
Abstract
We study Josephson junctions based on InSb nanowires with Sn shells. We observe skewed critical current diffraction patterns: the maxima in forward and reverse current bias are at different magnetic flux, with a displacement of 20-40 mT. The skew is greatest when the external field is nearly perpendicular to the nanowire, in the substrate plane. This orientation suggests that spin-orbit interaction plays a role. We develop a phenomenological model and perform tight-binding calculations, both methods reproducing the essential features of the experiment. The effect modeled is the $\phi$0-Josephson junction with higher-order Josephson harmonics. The system is of interest for Majorana studies: the effects are either precursor to or concomitant with topological superconductivity. Current-phase relations that lack inversion symmetry can also be used to design quantum circuits with engineered nonlinearity.
Author indications on fulfilling journal expectations
- Provide a novel and synergetic link between different research areas.
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- Detail a groundbreaking theoretical/experimental/computational discovery
- Present a breakthrough on a previously-identified and long-standing research stumbling block
Author comments upon resubmission
The authors thank all referees for their comments. We will be posting replies individually on SciPost. Because there is no color difference, we quote the referee’s comments with ‘>” . Report 1:
The referee’ss addressed most of my criticism, except for choosing their "preferred interpretation" for the origin of the Phi0 effect. Particularly, I would like to refer to [Davydova et al., Sci. Adv. 8, eabo0309 (2022)], where the authors propose a purely orbital origin for the anomalous Josephson effect. I expect this contribution to also depend on the direction of the magnetic field. Moreover, a recent work [Reinhardt, S., Ascherl, T., Costa, A. et al. Nat Commun 15, 4413 (2024)] argues that whereas an anomalous Josephson effect caused by SOC has a strong gate dependence, the orbital counterpart is mostly insensitive to the gate voltage. Since the authors claim that "effect is observed over wide ranges of gate voltage" and that "no consistent effect of gate voltage on the skew magnitude is observed", their observations seem consistent with orbital effects. Thus, it remains unclear to me why the authors "do not feel it [orbital effect] is a significant enough effect to change our preferred interpretation". I am keen to recommend the manuscript for publication if the authors provide enough data to justify their preferred explanation or give appropriate weight for alternative explanations. In fact, gate tunability of SOI in nanowires is not something we expect based on numerous previous measurements, the number for SOI comes out roughly the same. Any changes will be within the variations of our extracted skew. At the same time, spin-orbit anisotropy has been observed many times and the orientation of the anisotropy matches. The orbital effect would be comparable for either direction perpendicular to the nanowire while the spin-orbit effect is dramatically oriented perpendicular to the nanowire in the substrate plane. On a larger point, our paper provides both interpretations and gives arguments why we prefer the SOI one. It does not however suppress the other interpretation, and any reader can evaluate the results and their presentation and arrive at their own conclusions.
Report 2:
The authors have responded to my previous comments, but they have not addressed the clarifications I requested regarding the difference between Phi0 behavior and asymmetric CPR, nor have they addressed my criticism on the phenomenological model. Arguments based on authority, such as "Some of us have worked for many years on trying to unambiguously establish the Phi0 behavior" or personal preference, such as "Some of us find the Phi0 effect more interesting than SDE" do not adequately address my comments. I find that the authors are not being sufficiently receptive to my constructive feedback. Thus, after two refereeing rounds, I still cannot recommend publication of the manuscript in the present form but leave the final decision to the editors. We believe that the decision to refer to this phenomenon as a Phi0 junction or a superconducting diode should be left to the authors as a personal choice. We appreciate the discussion with the referee but wish to maintain the way we frame it in the paper.
List of changes
Add three references:
Ref. 19: J. S. Meyer and M. Houzet, Appl. Phys. Lett 125, 022603 (2024).
Ref.20 : S. Reinhardt, T. Ascherl, A. Costa, J. Berger, S. Gronin, G. C. Gardner, T. Lindemann, M. J. Manfra, J. Fabian, D. Kochan, et al., Nature Communications 15, 4413 (2024).
Ref.47: C. Owen and D. Scalapino, Physical Review 164, 538 (1967).
Current status:
Reports on this Submission
Report
I read the remaining criticism of both referees:
Referee 1 sees a stronger evidence for an orbital effect as opposed to a spin-orbit coupling as origin of the effect. The author‘s statement, that there is no SYSTEMATIC gate dependence, is taken as an absence of a gate dependence. Figure 6, however, displays a clear, but fluctuating gate variation of the diode efficiency, which is qualitatively reproduced by model calculations. I do not necessarily expect the same systematic gate dependence as in the cited work by Reinhardt et al., because the potential landscape in the nanowires is typically much more disordered when compared to 2DEGs. On the other hand, there seem to be no reasons for such fluctuations in the orbital effect proposed by Davydova et al. Hence, I support the author‘s point of view.
Referee 2 requests a clear discrimination between phi0-shift on one hand and anharmonic CPR on the other. In their discussion of Eq. 1, the authors clearly state that the diode effect results from the difference between the phi0-shifts of the first two harmonics of the CPR, while a sinusoidal CPR produces no diode effect. Even though their experiment is not sensitive to the global phi0-shift, it detects the relative shift \delta_12 via the diode effect. In my view, this is correct and clear enough.
For these reasons, I recommend acceptance of the manuscript in its present form.
Recommendation
Publish (easily meets expectations and criteria for this Journal; among top 50%)