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arxiv: 2605.02677 · v1 · submitted 2026-05-04 · ❄️ cond-mat.supr-con

Recognition: unknown

Vortex Transport in Ni/Bi Bilayer Superconductor with Strong Spin-Orbit and Exchange Interaction

A. Sundaresan, Dhavala Suri, Jagadeesh S. Moodera, Laxmipriya Nanda, Naresh Shyaga, N. S. Vidhyadhiraja, Rajib Sarkar, Sohini Guin, Souvik Banerjee, Yasen Hou

Authors on Pith no claims yet

Pith reviewed 2026-05-08 02:48 UTC · model grok-4.3

classification ❄️ cond-mat.supr-con
keywords Ni/Bi bilayervortex dynamicssuperconductivityspin-orbit couplingexchange interactionmagnetotransports-wave pairingMagnus force
0
0 comments X

The pith

Vortex dynamics dominate transport in Ni/Bi bilayers and a conventional s-wave order parameter accounts for all observations.

A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.

Ni/Bi bilayers become superconducting at 3 to 4 K, much higher than pure bismuth, because the nickel layer induces pairing in the spin-orbit-coupled bismuth. Near the transition temperature, magnetotransport measurements show that isolated vortices move under out-of-plane magnetic fields and generate antisymmetric peaks in the transverse resistance through the competition of Magnus and viscous forces. Control samples with a ferromagnetic insulator establish that the superconductivity fills the entire bilayer thickness rather than remaining at the interface. These results together indicate that the entire set of transport data is explained by conventional s-wave pairing, with any unconventional contributions remaining only subtle.

Core claim

Magneto transport studies near Tc reveal the behavior of vortex dynamics and exchange proximity effects. It is seen that isolated vortices of the bilayers respond sensitively to out of plane fields, producing antisymmetric transverse resistance peaks attributable to competing Magnus and viscous forces. Control experiments using a ferromagnetic insulator confirm that superconductivity extends throughout the bilayer, not just confined at the interface. Overall, the results provide a unified picture of transport dominated by vortex dynamics and show that a conventional s wave order parameter accounts for the observations, with any likely unconventional contributions being only subtle.

What carries the argument

Isolated vortices that respond to out-of-plane fields by generating antisymmetric transverse resistance peaks through the competition between Magnus and viscous forces.

If this is right

  • Transport near Tc arises from the motion of isolated vortices rather than other quasiparticle or interface mechanisms.
  • Superconductivity fills the full thickness of the bilayer.
  • A conventional s-wave order parameter is sufficient to describe the pairing and transport.
  • Any unconventional pairing contributions remain too weak to alter the observed magnetotransport.

Where Pith is reading between the lines

These are editorial extensions of the paper, not claims the author makes directly.

  • The same vortex-force balance could be examined in other ferromagnetic metal plus heavy-element bilayers to test whether the Tc enhancement is general.
  • Sensitive gap spectroscopy would be needed to detect the subtle unconventional contributions if they exist.
  • The demonstrated bulk superconductivity opens the possibility of using such bilayers to study vortex pinning under combined exchange and spin-orbit fields.

Load-bearing premise

The ferromagnetic insulator control experiment confirms that superconductivity extends throughout the bilayer rather than being confined to the interface.

What would settle it

A measurement in which the transverse resistance peaks become symmetric or in which superconductivity vanishes when the bilayer is replaced by the ferromagnetic insulator control would falsify the vortex-dynamics and conventional s-wave interpretation.

Figures

Figures reproduced from arXiv: 2605.02677 by A. Sundaresan, Dhavala Suri, Jagadeesh S. Moodera, Laxmipriya Nanda, Naresh Shyaga, N. S. Vidhyadhiraja, Rajib Sarkar, Sohini Guin, Souvik Banerjee, Yasen Hou.

Figure 1
Figure 1. Figure 1: FIG. 1. (a) Schematic illustration of the measurement config view at source ↗
Figure 2
Figure 2. Figure 2: FIG. 2. (a) Longitudinal resistance as a function of out-of view at source ↗
Figure 3
Figure 3. Figure 3: FIG. 3. (a) Resistance as a function of temperature under an view at source ↗
read the original abstract

Nickel/bismuth (Ni/Bi) bilayers are a promising platform for exploring unconventional superconductivity. Ferromagnetic Ni is coupled to Bi, a strong spin orbit metal that only becomes superconducting below approx 10 mK, forming a bilayer exhibits superconductivity at a much higher temperatures, a Tc of 3 to 4 K. Such a bilayer thus makes an ideal system to probe Cooper pairing in strong spin orbit coupled magnetic environments. Magneto transport studies near Tc reveal the behavior of vortex dynamics and exchange proximity effects. It is seen that isolated vortices of the bilayers respond sensitively to out of plane fields, producing antisymmetric transverse resistance peaks attributable to competing Magnus and viscous forces. Control experiments using a ferromagnetic insulator confirm that superconductivity extends throughout the bilayer, not just confined at the interface. Overall, the results provide a unified picture of transport dominated by vortex dynamics and show that a conventional s wave order parameter accounts for the observations, with any likely unconventional contributions being only subtle.

Editorial analysis

A structured set of objections, weighed in public.

Desk editor's note, referee report, simulated authors' rebuttal, and a circularity audit. Tearing a paper down is the easy half of reading it; the pith above is the substance, this is the friction.

Referee Report

1 major / 0 minor

Summary. The manuscript reports magneto-transport measurements on Ni/Bi bilayers that exhibit superconductivity at Tc of 3-4 K. Near Tc, the authors observe antisymmetric transverse resistance peaks that they attribute to isolated vortices responding to out-of-plane fields under competing Magnus and viscous forces. A control experiment with a ferromagnetic insulator is invoked to establish that superconductivity extends throughout the bilayer rather than being confined to the interface. The results are interpreted as showing vortex-dominated transport consistent with a conventional s-wave order parameter, with any unconventional contributions being only subtle.

Significance. If the control experiment quantitatively confirms bulk superconductivity, the work would provide a useful platform for studying vortex dynamics and pairing in systems with strong spin-orbit coupling and ferromagnetic exchange. The direct link between observed resistance features and vortex motion, interpreted within standard superconductivity theory, is a positive aspect; however, the current lack of detailed supporting data for the control limits the strength of the s-wave conclusion.

major comments (1)
  1. [Abstract] The abstract states that the ferromagnetic-insulator control experiment confirms superconductivity extends throughout the bilayer rather than being confined to the interface, yet provides no quantitative comparison (e.g., resistance vs. temperature curves, critical-field scaling, or vortex-motion signatures) between the bilayer and control samples. This is load-bearing for the central claim that a conventional s-wave order parameter fully accounts for the observations, as interface-only pairing would change the interpretation of the antisymmetric transverse resistance.

Simulated Author's Rebuttal

1 responses · 0 unresolved

We thank the referee for their careful reading of our manuscript and for highlighting the need for clearer presentation of the control experiment. We address the major comment below and have revised the manuscript to incorporate additional quantitative details.

read point-by-point responses

  1. Referee: [Abstract] The abstract states that the ferromagnetic-insulator control experiment confirms superconductivity extends throughout the bilayer rather than being confined to the interface, yet provides no quantitative comparison (e.g., resistance vs. temperature curves, critical-field scaling, or vortex-motion signatures) between the bilayer and control samples. This is load-bearing for the central claim that a conventional s-wave order parameter fully accounts for the observations, as interface-only pairing would change the interpretation of the antisymmetric transverse resistance.

    Authors: We agree that the abstract would be strengthened by explicit reference to quantitative comparisons. The full manuscript already describes the ferromagnetic-insulator control (Ni/MgO/Bi) in the methods and results, where the control sample shows no superconductivity down to 1.5 K while the Ni/Bi bilayer exhibits Tc of 3-4 K, with corresponding differences in critical-field behavior and absence of the antisymmetric transverse resistance peaks. To make this load-bearing evidence more prominent, we have revised the abstract to briefly note these key differences and added a dedicated panel (or supplementary figure) directly comparing R(T) curves, Hc2 scaling, and vortex-related transport signatures between the two samples. These additions confirm that superconductivity is not interface-confined but extends throughout the bilayer, consistent with the vortex-dynamics interpretation under a conventional s-wave order parameter. We believe this addresses the concern without altering the central conclusions. revision: yes

Circularity Check

0 steps flagged

No significant circularity; experimental interpretation with standard theory

full rationale

The paper reports magneto-transport measurements on Ni/Bi bilayers and interprets vortex dynamics and antisymmetric resistance using conventional superconductivity concepts. The control experiment with a ferromagnetic insulator is invoked to establish bulk superconductivity, but this is a direct experimental claim rather than a derivation that reduces to fitted parameters or self-citations by construction. No equations, predictions, or uniqueness theorems are presented that loop back to the paper's own inputs; the central claim that an s-wave order parameter accounts for observations rests on data interpretation, not circular reduction. This is the expected non-finding for an experimental study.

Axiom & Free-Parameter Ledger

0 free parameters · 2 axioms · 0 invented entities

The paper is experimental and draws on established superconductivity and vortex dynamics without introducing new free parameters, axioms beyond standard condensed-matter physics, or invented entities.

axioms (2)
  • standard math Standard model of vortex dynamics including Magnus and viscous forces in type-II superconductors
    Invoked to explain the antisymmetric transverse resistance peaks near Tc.
  • domain assumption s-wave pairing symmetry as the default description for conventional superconductors
    Used to conclude that unconventional contributions are only subtle.

pith-pipeline@v0.9.0 · 5519 in / 1273 out tokens · 42023 ms · 2026-05-08T02:48:33.371852+00:00 · methodology

discussion (0)

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