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Large Second-Order Josephson Effect in Planar Superconductor-Semiconductor Junctions
by P. Zhang, A. Zarassi, L. Jarjat, V. Van de Sande, M. Pendharkar, J. S. Lee, C. P. Dempsey, A. P. McFadden, S. D. Harrington, J. T. Dong, H. Wu, A. -H. Chen, M. Hocevar, C. J. Palmstrøm, S. M. Frolov
This Submission thread is now published as
Submission summary
| Authors (as registered SciPost users): | Sergey Frolov · Po Zhang |
| Submission information | |
|---|---|
| Preprint Link: | https://arxiv.org/abs/2211.07119v3 (pdf) |
| Code repository: | https://zenodo.org/record/6416083 |
| Data repository: | https://zenodo.org/record/6416083 |
| Date accepted: | 2023-12-18 |
| Date submitted: | 2023-11-21 15:36 |
| Submitted by: | Zhang, Po |
| Submitted to: | SciPost Physics |
| Ontological classification | |
|---|---|
| Academic field: | Physics |
| Specialties: |
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| Approaches: | Experimental, Computational |
Abstract
We investigate the current-phase relations of Al/InAs-quantum well planar Josephson junctions fabricated using nanowire shadowing technique. Based on several experiments, we conclude that the junctions exhibit an unusually large second-order Josephson harmonic, the $\sin(2\varphi)$ term. First, superconducting quantum interference devices (dc-SQUIDs) show half-periodic oscillations, tunable by gate voltages as well as magnetic flux. Second, Josephson junction devices exhibit kinks near half-flux quantum in supercurrent diffraction patterns. Third, half-integer Shapiro steps are present in the junctions. Similar phenomena are observed in Sn/InAs quantum well devices. We perform data fitting to a numerical model with a two-component current phase relation. Analysis including a loop inductance suggests that the sign of the second harmonic term is negative. The microscopic origins of the observed effect remain to be understood. We consider alternative explanations which can account for some but not all of the evidence.
List of changes
In the abstract, we added "Analysis including a loop inductance suggests that the sign of the second harmonic term is negative."
In "Background: Current Phase Relations", we added a discussion about higher-order harmonics in SIS junctions.
In "Previous Work: Second Order Josephson Effect", we added a discussion about SQUIDs flux-biased to pi.
In "List of Results", we added sentences about the sign of the second harmonic.
In "Figure 1 Description", we added "The long effective length is likely due to large London penetration depth which is typical for thin film superconductors."
We added Fig. 6 and renamed "Non-identical negative and positive switching currents" to "Figure 6 Discussion". We added discussions about the inductive effect and the sign of the second harmonic term in this block.
In the supplementary, we added sections "Inductive SQUID" and "Sign of the second harmonic term" (including Figs. S5-S8). We added Fig. S9, which shows the zoomed-in data of Figs. 2(a) and 3(a).
Other changes.
Published as SciPost Phys. 16, 030 (2024)
Reports on this Submission
Report
The authors have properly taken my suggestions into account. Especially the inductance contribution to the transport data is now properly addressed.
The only question I still have is why the authors consider flux focusing as an explanation of the large obtained effective junction area to be "heuristic" and rather stick to interpreting the large junction area as coming from a large penetration depth.
But this does not withhold me from recommending this work to be published.
Carlo Beenakker on 2023-11-21 [id 4139]
This is the second report of a referee from round one, entered here by the editor because of an issue with the SciPost interface:
I thank the Authors for their clarifications and modifications to the manuscript. They are all clear to me, except the reply to point (5).
"This is actually very standard and related to the London penetration depth. Not related to new physics."
To say that something is "very standard" is, byt itself, no explanation. I think the Authors should expand on this, if needed through providing references; if they have a very standard explanation of their remark, it should be added to the text.
Other than this point, I think the paper is ready for publication.