SciPost Submission Page
Zero-bias conductance peaks at zero applied magnetic field due to stray fields from integrated micromagnets in hybrid nanowire quantum dots
by Y. Jiang, M. Gupta, C. Riggert, M. Pendharkar, C. Dempsey, J. S. Lee, S. D. Harrington, C. J. Palmstrøm, V. S. Pribiag, S. M. Frolov
Submission summary
| Authors (as registered SciPost users): | Sergey Frolov |
| Submission information | |
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| Preprint Link: | https://arxiv.org/abs/2305.19970v1 (pdf) |
| Data repository: | https://zenodo.org/records/7988096 |
| Date submitted: | 2025-02-12 16:56 |
| Submitted by: | Frolov, Sergey |
| Submitted to: | SciPost Physics |
| Ontological classification | |
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| Academic field: | Physics |
| Specialties: |
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| Approach: | Experimental |
Abstract
Many recipes for realizing topological superconductivity rely on broken time-reversal symmetry, which is often attained by applying a substantial external magnetic field. Alternatively, using magnetic materials can offer advantages through low-field operation and design flexibility on the nanoscale. Mechanisms for lifting spin degeneracy include exchange coupling, spin-dependent scattering, spin injection-all requiring direct contact between the bulk or induced superconductor and a magnetic material. Here, we implement locally broken time-reversal symmetry through dipolar coupling from nearby micromagnets to superconductor-semiconductor hybrid nanowire devices. Josephson supercurrent is hysteretic due to micromangets switching. At or around zero external magnetic field, we observe an extended presence of Andreev bound states near zero voltage bias. We also show a zero-bias peak plateau of a non-quantized value. Our findings largely reproduce earlier results where similar effects were presented in the context of topological superconductivity in a homogeneous wire, and attributed to more exotic time-reversal breaking mechanisms [1]. In contrast, our stray field profiles are not designed to create Majorana modes, and our data are compatible with a straightforward interpretation in terms of trivial states in quantum dots. At the same time, the use of micromagnets in hybrid superconductor-semiconductor devices shows promise for future experiments on topological superconductivity.
Author indications on fulfilling journal expectations
- Provide a novel and synergetic link between different research areas.
- Open a new pathway in an existing or a new research direction, with clear potential for multi-pronged follow-up work
- Detail a groundbreaking theoretical/experimental/computational discovery
- Present a breakthrough on a previously-identified and long-standing research stumbling block
Current status:
Reports on this Submission
Report #1 by Helene Bouchiat (Referee 1) on 2025-4-4 (Invited Report)
Report
This paper presents interesting data on the magneto-transport of in hybrid junctions based on semiconducting nanowires with important Rashba spin-orbit interactions, coupled to superconducting electrodes. These devices have been considered as possible good candidates for the investigation of the physics of Majorana modes when a magnetic field is applied along the nanowires axis or when they are covered by an insulating magnetic layer in both cases opening a spin-orbit gap. The present experiments rely on the implementation of nanomagnets in close vicinity of the nanowires which create stray magnetic fields on the hybrid devices.
The motivation of this work is to reveal the effect of the stray field spatial variations of these nanomagnets on the transport properties of the nanowires reproducing previous controversial data considered as signatures of the existence of Majorana modes and topological superconductivity. Among these signatures is the existence of zero bias differential conductance peaks which are expected to be exactly quantised to the value of e2/h, half of the conductance quantum and was considered as a “smoking gun” proving the existence of Majorana modes in InAs an InSb nanowires. The paper is organised as follows:
-1The authors first present data on a device connected at each end to aluminium electrodes showing the existence of magnetic hysteresis in the critical current in relation of the stray field induced by the nanomagnets.
-2 A second sample connected to one normal and one superconducting electrode, exhibits a zero bias conductance peak between e2/h and 2e2/h at zero magnetic field which is split depending on the gate voltage. Similar features are observed in finite field depending on its orientation and the the magnetic history of the nanomagnet.
-3 Other examples are shown in the supplemental material section. The authors show that, by tuning the magnetic field environment and gate voltage, it is possible to observe a zero bias conductance peak whose amplitude is very close the theoretically predicted value for Majorana modes, even if the investigated devices are in a range of chemical potential and magnetic field parameters where this physics of topological superconductivity is not relevant. These results are important and show the extreme difficulties to obtain conclusive experimental results in this field.
-4 The authors finally emphasize the important fact that the magnetic texture around the wires can be designed in principle at will, using micromagnetic simulations. The obtained results therefore demonstrate the possibility to use nanomagnets to control precisely the magnetic field environment of hybrid NS nano-devices and offer a promising tool to investigate their potentialities concerning the observation of Majorana modes and topological superconductivity.
In that sense this paper “opens a new pathway in an existing or a new research direction, with clear potential for multi-pronged follow-up work”
-5 However at this stage even if the points risen by the authors are very important and justify publication of this work, it would have been nice to have a more precise discussion of the reproducibility of the results obtained within one device and the variability of the results obtained in the different investigated devices. I strongly encourage the authors to provide such a synthesis of their work before publication in SciPost.
Requested changes
Even if the points risen by the authors are very important and justify publication of this work, it would have been nice to have a more precise discussion of the reproducibility of the results obtained within one device and the variability of the results obtained in the different investigated devices. I strongly encourage the authors to provide such a synthesis of their work before publication in SciPost.
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