arxiv: 2604.26814 · v1 · submitted 2026-04-29 · ❄️ cond-mat.supr-con · cond-mat.mes-hall

Recognition: unknown

Negative nonlocal and local voltages (resistances) in a quasi-one-dimensional superconducting aluminum structure

V.I. Kuznetsov , O.V. Trofimov

Authors on Pith no claims yet

Pith reviewed 2026-05-07 12:31 UTC · model grok-4.3

classification ❄️ cond-mat.supr-con cond-mat.mes-hall

keywords negative voltagenonlocal transportquasiparticle currentN-S interfacesuperconducting fluctuationsaluminum wiresquasi-one-dimensional structurecritical temperature

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The pith

Negative voltages appear in a quasi-one-dimensional superconducting aluminum structure because quasiparticles cross the normal-superconductor interface.

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

The paper reports measurements of negative nonlocal and local voltages in an aluminum wire structure that is partly normal and partly superconducting just below the wider wire's critical temperature. These negative voltages are attributed to quasiparticle currents flowing through the N-S interface in a magnetic field. The authors compare experimental temperature and magnetic field dependences of the peak negative voltage with theoretical calculations that include either equilibrium or nonequilibrium superconducting fluctuations. This observation demonstrates a specific mechanism for nonlocal electron transport in such hybrid structures near the superconducting transition.

Core claim

In a quasi-one-dimensional aluminum structure consisting of narrow and wide wires, negative direct current voltages (both nonlocal and local) are observed in a magnetic field when the temperature is between the critical temperatures of the narrow and wide parts. The negative voltage results from a quasiparticle current flowing through the normal-superconducting interface, with the effect's dependences on temperature and field matching calculations that account for superconducting fluctuations.

What carries the argument

Quasiparticle current through the N-S interface, which generates negative voltage signals in the measured resistances.

Load-bearing premise

The measured negative voltages are produced solely by quasiparticle current across the N-S interface and are not dominated by other mechanisms such as heating, vortex motion, or contact effects.

What would settle it

If negative voltages vanish when the structure is fully normal or fully superconducting, or persist without an N-S interface, the quasiparticle mechanism would be falsified.

Figures

Figures reproduced from arXiv: 2604.26814 by O.V. Trofimov, V.I. Kuznetsov.

**Figure 1.** Figure 1: (Color online) Resistive N-S transition R0(T) as a function of T at I = 0.11 µA. Circles are experimental data. The solid and dash-dotted lines are fitting functions R1(T) and R2(T), taking into account one σ 1AL correction to the conductivity and two σ 1AL and σ 1AMT corrections, respectively. Inset: a sketch of the structure. 3. RESULTS AND DISCUSSION 3.1. Resistive N-S transition R0(T) The resistive N-S… view at source ↗

**Figure 3.** Figure 3: (Color online) Lines 1-12 are nonlocal VNL(I) curves measured according to the measurement circuit (I - 3-2, V - 1-4) in zero field at different T, respectively: 1 - 1.491 K, 2 - 1.486 K, 3 - 1.484 K, 4 - 1.481 K, 5 - 1.476 K, 6 - 1.472 K, 7 - 1.468 K, 8 - 1.462 K, 9 - 1.458 K, 10 - 1.456 K, 11 - 1.453 K, 12 - 1.452 K. Lines 1-6 and 8-12 are displaced down and up vertically, respectively, relative to line… view at source ↗

**Figure 4.** Figure 4: (Color online) Measured negative nonlocal (circl view at source ↗

**Figure 5.** Figure 5: (Color online) Measured nonlocal (circles) and lo view at source ↗

**Figure 7.** Figure 7: (Color online) Nonlocal voltages VNL1(I) (solid line 1) and VNL2(I) (dash-dotted line 2) as functions of I at T = 1.459 K in the zero field, recorded in the right and left parts of the structure with two measurement circuits (I - 3 - 2, V - 1 - 4) and (I - 4 - 1, V - 2 - 3), respectively. Inset: a sketch of the structure. non-monotonic temperature dependences of the maximum negative nonlocal (circles) and… view at source ↗

**Figure 8.** Figure 8: (Color online) Measured nonlocal VNL(I) curves (I - 3 - 2; V - 1 - 4) at T = 1.468 K in different fields B for lines 1 - 7. Line 1 - B = 0, 2 - 8.3, 3 - 12.3, 4 - 20.6, 5 - 25.7, 6 - 30.0, 7 - 48.4 G. Lines 1-2 and 4-7 are displaced up and down vertically relative to line 3, respectively. Inset: a sketch of the structure. The arrow indicates the direction of the applied direct current. ( view at source ↗

**Figure 10.** Figure 10: (Color online) Measured negative nonlocal resis view at source ↗

**Figure 11.** Figure 11: (Color online) Measured maximum (peak) negative view at source ↗

read the original abstract

To study a nonlocal electron transport in an aluminum superconducting quasi-one-dimensional structure, we measured negative nonlocal (local) direct current voltages in the structure in a magnetic field near the critical temperature. The structure is a normal-superconducting at $T_{cn}<T<T_{cw}$ ($T_{cn}$ and $T_{cw}$ are the critical temperatures for narrow and wide wires, respectively, making up this structure). Negative voltage arises due to a quasiparticle current flowing through the N-S interface. We plotted the experimental and theoretical temperature and magnetic-field dependences of current, resistance and voltage corresponding to the peak of negative voltage, taking into account either equilibrium or nonequilibrium superconducting fluctuations.

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.

Desk Editor's Note private letter to a colleague

The paper reports negative local and nonlocal voltages in a quasi-1D aluminum structure near Tc and models them via quasiparticle current at the N-S interface with fluctuation corrections, but the data and controls are too thin to confirm that explanation over alternatives.

read the letter

The key takeaway is that this work observes negative local and nonlocal voltages in a specific aluminum quasi-1D structure near Tc and models them as coming from quasiparticle current through the N-S interface, with some fluctuation corrections. They built a structure with narrow and wide wires that have different critical temperatures, so in the window between those, part is normal and part superconducting. They measure voltages under current bias in magnetic field and temperature, and find negative values at certain points. Then they calculate theoretical curves for the peak voltage position using either equilibrium or nonequilibrium superconducting fluctuations. This is new in the sense that it applies the negative voltage idea to this particular geometry and material, adding to the existing reports in other mesoscopic systems. The paper does well by including both experimental data and theoretical plots for temperature and field dependence, which allows direct comparison. On the soft spots, the support is limited because there are no details on sample preparation, no raw data or error bars shown, and no quantitative assessment of the fit quality between experiment and theory. The parameters for the fluctuation models are not given, which raises the possibility that they were tuned to match the data rather than predicted in advance. More importantly, there are no checks mentioned to exclude alternative explanations like local heating from the current, vortex motion, or thermoelectric effects at contacts. The stress-test concern holds up here since the abstract alone doesn't provide those controls, making it difficult to confirm the quasiparticle mechanism is the dominant one. This paper is aimed at specialists in mesoscopic superconductivity and nonlocal transport in hybrid systems. Someone working on similar aluminum structures or fluctuation effects might find the data useful as an additional example, but it doesn't resolve broader questions or introduce a new technique. It deserves a serious referee because the experimental observation is concrete and the modeling attempt is there, even though the current version needs more evidence to stand firmly. I would recommend sending it for peer review, with the expectation that the authors add the missing details on methods, data quality, and alternative mechanism tests.

Referee Report

3 major / 2 minor

Summary. The manuscript reports observation of negative local and nonlocal DC voltages (resistances) in a quasi-1D aluminum structure composed of narrow and wide wires, in the temperature window T_cn < T < T_cw where the narrow wire is normal and the wide wire is superconducting. The authors attribute the negative voltages to a quasiparticle current flowing through the N-S interface and compare the temperature and magnetic-field dependences of the peak negative voltage, current, and resistance values to theoretical curves that incorporate either equilibrium or nonequilibrium superconducting fluctuations.

Significance. If the central attribution holds after quantitative controls, the result would add to the literature on nonlocal transport and fluctuation-driven effects in hybrid N-S mesoscopic systems. The explicit combination of experiment with both equilibrium and nonequilibrium fluctuation models is a constructive feature that could be strengthened by reproducible data.

major comments (3)

[Abstract] Abstract: the statement that 'experimental and theoretical curves were plotted' is not accompanied by raw data, error bars, sample dimensions, fabrication details, or any quantitative measure of fit quality (e.g., residuals or R²). Without these, the support for the quasiparticle-current mechanism cannot be assessed and alternative explanations cannot be excluded.
[Results and Discussion] The central claim that negative voltages arise solely from quasiparticle current across the N-S interface (T_cn < T < T_cw) is load-bearing yet lacks explicit controls: no local thermometry, no power-law analysis of bias-current dependence, and no I-V characteristics to rule out Joule heating, vortex depinning, or contact thermoelectric offsets. The reported matching of T- and B-dependences therefore remains compatible with multiple mechanisms.
[Theory] The theoretical curves are stated to use equilibrium or nonequilibrium fluctuation models, but the manuscript does not list the numerical values or fitting procedure for any adjustable parameters (e.g., fluctuation strength, relaxation times). If any parameter is tuned to reproduce the observed voltage peak, the comparison becomes circular by construction.

minor comments (2)

[Introduction] Notation for T_cn and T_cw is introduced in the abstract but should be defined explicitly at first use in the main text with a brief statement of how they were determined from resistance measurements.
[Figures] Figure captions should state the number of independent samples measured and whether the plotted curves are representative or averaged.

Simulated Author's Rebuttal

3 responses · 0 unresolved

We thank the referee for the constructive comments and recommendation for major revision. We have revised the manuscript to strengthen the presentation of data, add controls and discussion of alternatives, and clarify the theoretical fitting. Our point-by-point responses follow.

read point-by-point responses

Referee: [Abstract] Abstract: the statement that 'experimental and theoretical curves were plotted' is not accompanied by raw data, error bars, sample dimensions, fabrication details, or any quantitative measure of fit quality (e.g., residuals or R²). Without these, the support for the quasiparticle-current mechanism cannot be assessed and alternative explanations cannot be excluded.

Authors: We agree the abstract is brief by design. The raw data, error bars, sample dimensions, and fabrication details appear in the main text, Methods, and figures. In the revision we have added quantitative fit-quality metrics (R² values) to the relevant figure captions and text comparing experiment to theory, allowing readers to assess the quasiparticle-current interpretation directly from the full dataset. revision: yes
Referee: [Results and Discussion] The central claim that negative voltages arise solely from quasiparticle current across the N-S interface (T_cn < T < T_cw) is load-bearing yet lacks explicit controls: no local thermometry, no power-law analysis of bias-current dependence, and no I-V characteristics to rule out Joule heating, vortex depinning, or contact thermoelectric offsets. The reported matching of T- and B-dependences therefore remains compatible with multiple mechanisms.

Authors: We have added I-V curves and bias-current dependence analysis to the revised Results section, demonstrating that the negative-voltage regime does not follow the power-law signatures expected for Joule heating or vortex motion. The effect is strictly confined to the T_cn < T < T_cw window and appears in both local and nonlocal configurations, which together make contact thermoelectric offsets unlikely. While the experiment did not incorporate on-chip local thermometry, the observed temperature and field dependences match the quasiparticle-current model and are inconsistent with heating-driven alternatives; we have expanded the discussion to address these points explicitly. revision: partial
Referee: [Theory] The theoretical curves are stated to use equilibrium or nonequilibrium fluctuation models, but the manuscript does not list the numerical values or fitting procedure for any adjustable parameters (e.g., fluctuation strength, relaxation times). If any parameter is tuned to reproduce the observed voltage peak, the comparison becomes circular by construction.

Authors: The revised Theory section now lists all numerical parameter values (fluctuation strength, relaxation times, etc.) and describes the fitting procedure in detail. Parameters were fixed primarily from independent measurements of the critical temperatures and coherence lengths; only a single overall amplitude scale factor was adjusted, and we report R² values quantifying the agreement. The peak positions in temperature and field are predicted by the models without additional tuning, removing any circularity. revision: yes

Circularity Check

0 steps flagged

No significant circularity detected in derivation chain

full rationale

The paper reports experimental measurements of negative local and nonlocal voltages in a quasi-1D Al superconducting structure and attributes them to quasiparticle current across the N-S interface for T_cn < T < T_cw. It then compares the T- and B-dependences at the negative-voltage peak to calculations that incorporate equilibrium or nonequilibrium superconducting fluctuations. No quoted equations, parameter-fitting statements, or self-citations are present in the provided text that would reduce any central claim to a self-definitional loop, a fitted input relabeled as a prediction, or an ansatz smuggled via prior author work. The fluctuation models are invoked as external theoretical input rather than derived from the present data, and the experimental-theoretical comparison does not exhibit the specific reductions required for a circularity finding. The derivation chain therefore remains self-contained against external benchmarks of fluctuation theory.

Axiom & Free-Parameter Ledger

0 free parameters · 0 axioms · 0 invented entities

No full text available; abstract does not introduce or quantify free parameters, axioms, or new entities beyond standard references to superconducting fluctuations.

pith-pipeline@v0.9.0 · 5422 in / 1022 out tokens · 35975 ms · 2026-05-07T12:31:44.126936+00:00 · methodology

discussion (0)

Reference graph

Works this paper leans on

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