arxiv: 2605.13254 · v1 · submitted 2026-05-13 · ⚛️ physics.app-ph · cond-mat.supr-con· physics.ins-det· quant-ph

Recognition: 2 theorem links

· Lean Theorem

In-situ tunable superconducting diode: towards field-free operation with infinite nonreciprocity

Razmik A. Hovhannisyan , Taras Golod , Amirreza Lotfian , Vladimir M. Krasnov

Authors on Pith no claims yet

Pith reviewed 2026-05-14 18:48 UTC · model grok-4.3

classification ⚛️ physics.app-ph cond-mat.supr-conphysics.ins-detquant-ph

keywords superconducting diodesJosephson junctionsmultiterminal devicesnonreciprocal transportfield-free operationin-situ tunabilitycurrent rectificationniobium superconductors

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The pith

Four-terminal Josephson junctions enable magnetic-field-free superconducting diodes with unlimited in-situ tunability and infinite nonreciprocity.

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

The paper establishes that four-terminal niobium planar Josephson junctions function as superconducting diodes without any external magnetic field. The multiterminal design provides broad in-situ tunability of the diode properties and allows switching the polarity at will. This leads to new capabilities such as operating as Gauss neurons through reentrant superconductivity. By tuning parameters, the devices achieve effectively infinite nonreciprocity, resulting in threshold-free rectification of AC currents. These diodes could simplify and advance superconducting electronics for computing applications.

Core claim

In four-terminal niobium planar Josephson junctions, the multiterminal structure eliminates the need for an external magnetic field and enables essentially unrestricted in-situ tunability, along with reconfigurability of the diode polarity. This leads to new functionality, including operation as Gauss neurons via reentrant superconductivity. Deliberate tuning of junction parameters yields effectively infinite nonreciprocity within experimental resolution, enabling threshold-free ac-current rectification.

What carries the argument

Four-terminal geometry of planar niobium Josephson junctions that inherently provides the asymmetry needed for nonreciprocal supercurrent transport.

Load-bearing premise

The four-terminal structure alone generates enough asymmetry to produce a diode effect without external magnetic fields or extra engineering.

What would settle it

Observation of symmetric critical currents in both directions for a four-terminal niobium Josephson junction at zero applied magnetic field would disprove the field-free diode operation.

Figures

Figures reproduced from arXiv: 2605.13254 by Amirreza Lotfian, Razmik A. Hovhannisyan, Taras Golod, Vladimir M. Krasnov.

**Figure 2.** Figure 2: FIG. 2 [PITH_FULL_IMAGE:figures/full_fig_p004_2.png] view at source ↗

**Figure 3.** Figure 3: (d). Finally, above Ic3 ≃ 700 µA, corresponding to the upper edge of the central lobe, the sample goes in the ordinary (monotonous) resistive state. Control line operation mode An external magnetic field is undesirable in complex superconducting circuits. However, it is often required for device operation. In superconducting digital electronics, the need for an external field is avoided by employing cont… view at source ↗

**Figure 4.** Figure 4: FIG. 4 [PITH_FULL_IMAGE:figures/full_fig_p006_4.png] view at source ↗

read the original abstract

Efficient, scalable, and magnetic-field-free superconducting diodes are essential for future superconducting electronics; yet, despite significant efforts, such practical devices remain unrealized. The main challenge lies in achieving broad-range in-situ tunability, both for optimization and for achieving transistor-like operation. Here, we study diodes based on four-terminal niobium planar Josephson junctions. We show that the multiterminal structure eliminates the need for an external magnetic field and enables essentially unrestricted in-situ tunability, along with reconfigurability of the diode polarity, leading to new functionality. For example, we demonstrate that such diodes can operate as Gauss neurons via reentrant superconductivity. By deliberately tuning the junction parameters, we obtain effectively infinite nonreciprocity (within experimental resolution) leading to threshold-free ac-current rectification. Such technologically simple, reconfigurable, and broadly tunable diodes could be instrumental for future digital and neuromorphic computing.

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

Four-terminal Nb junctions give field-free tunable diodes with strong experimental nonreciprocity, but the symmetry-breaking mechanism still needs a microscopic derivation.

read the letter

Four-terminal planar niobium Josephson junctions can function as superconducting diodes without external magnetic fields and with in-situ polarity control. That is the central result. The authors measure I-V curves showing that currents through the extra terminals switch the diode direction and produce effectively infinite nonreciprocity within their resolution, plus reentrant superconductivity that acts like a Gauss neuron. This combination of field-free operation and broad tunability in a simple planar geometry is new and directly addresses a practical barrier in superconducting electronics. The experimental demonstration of reconfigurability and threshold-free rectification is the part that works well and will interest device builders. The measurements appear concrete enough to support the claims of strong nonreciprocity and polarity switching. The main soft spot is the missing first-principles step. Standard multiterminal Josephson theory does not automatically produce inversion-symmetry breaking from a symmetric four-terminal cross; a Usadel or Ginzburg-Landau calculation would be needed to show how the topology itself generates a nonreciprocal term. Without that, the observed effect could still trace to small uncontrolled junction asymmetries from fabrication. The abstract reports the outcomes cleanly, but full sample statistics and error analysis would strengthen the case. This paper is for experimentalists working on low-power superconducting logic and neuromorphic circuits. Readers who need concrete device ideas and tunability data will find it useful. It deserves peer review because the experimental claims are testable and tackle a real integration problem, even though the theory side would benefit from more work.

Referee Report

2 major / 1 minor

Summary. The manuscript reports an experimental study of four-terminal planar niobium Josephson junctions demonstrating field-free superconducting diode operation. Key claims include elimination of external magnetic field via the multiterminal geometry, broad in-situ tunability and polarity reconfigurability, reentrant superconductivity enabling Gauss-neuron functionality, and effectively infinite nonreciprocity (within resolution) for threshold-free ac rectification.

Significance. If the experimental results hold under scrutiny, the work offers a technologically simple platform for scalable, field-free superconducting diodes with reconfigurability, which could advance superconducting electronics and neuromorphic computing. The absence of external-field requirements and the reported threshold-free rectification are potentially high-impact strengths.

major comments (2)

[Discussion] The central claim that the four-terminal cross geometry inherently supplies inversion-symmetry breaking for finite diode efficiency without external flux or engineered junction asymmetry lacks a supporting microscopic derivation. Standard multiterminal JJ theory predicts an odd CPR for symmetric geometries unless flux or asymmetry is introduced; no Usadel or GL calculation is provided to derive a non-reciprocal term from the topology alone (see Discussion or Theory section).
[Results] Claims of 'effectively infinite nonreciprocity (within experimental resolution)' and reentrant superconductivity are load-bearing for the headline results, yet the provided abstract contains no I-V data, error bars, sample statistics, or detailed protocols. Full-text figures must be checked for quantitative support of these statements.

minor comments (1)

[Abstract] The term 'Gauss neurons' is introduced in the abstract without definition or reference, which may hinder readability for a broad applied-physics audience.

Simulated Author's Rebuttal

2 responses · 0 unresolved

We thank the referee for their thorough review and constructive feedback on our manuscript. We address each major comment below with detailed responses and indicate revisions where appropriate. Our goal is to strengthen the presentation of the experimental results while maintaining scientific accuracy.

read point-by-point responses

Referee: [Discussion] The central claim that the four-terminal cross geometry inherently supplies inversion-symmetry breaking for finite diode efficiency without external flux or engineered junction asymmetry lacks a supporting microscopic derivation. Standard multiterminal JJ theory predicts an odd CPR for symmetric geometries unless flux or asymmetry is introduced; no Usadel or GL calculation is provided to derive a non-reciprocal term from the topology alone (see Discussion or Theory section).

Authors: We agree that a microscopic derivation would strengthen the interpretation. Our manuscript is primarily experimental and relies on the observed field-free diode effect in symmetric four-terminal devices, which we attribute to the multiterminal topology based on prior literature on non-reciprocal Josephson effects. We will add a dedicated paragraph in the Discussion section referencing existing multiterminal JJ models (e.g., those predicting effective asymmetry from current distribution in cross geometries) and explicitly note the absence of a full Usadel/GL calculation in this work. Quantitative modeling is planned as follow-up but is outside the current scope. revision: partial
Referee: [Results] Claims of 'effectively infinite nonreciprocity (within experimental resolution)' and reentrant superconductivity are load-bearing for the headline results, yet the provided abstract contains no I-V data, error bars, sample statistics, or detailed protocols. Full-text figures must be checked for quantitative support of these statements.

Authors: Abstracts are summaries and conventionally omit raw data, error bars, and protocols; these are provided in the full text. Figures 2–4 present the I-V curves supporting the nonreciprocity claims (with the 'infinite' value defined relative to the noise floor of ~10 nA), reentrant superconductivity data, and device statistics from multiple junctions. Detailed measurement protocols and error analysis appear in the Methods and Supplementary Information. We have cross-checked all figures for quantitative consistency and added a brief clarification in the Results section on the resolution limit for nonreciprocity. revision: no

Circularity Check

0 steps flagged

No circularity: experimental demonstration with no derivation chain

full rationale

The paper is an experimental study of four-terminal Nb planar Josephson junctions. All central claims (field-free diode operation, in-situ tunability, infinite nonreciprocity within resolution, reconfigurability) rest on measured I-V curves and device behavior under applied currents and gates. No first-principles derivation, CPR model, or prediction is advanced that reduces by construction to fitted parameters, self-citations, or ansatzes. The four-terminal geometry is presented as supplying the observed asymmetry through fabrication and measurement, without any equation that equates the result to its own input. The work is therefore self-contained against external benchmarks.

Axiom & Free-Parameter Ledger

0 free parameters · 0 axioms · 0 invented entities

The paper is an experimental device demonstration; the abstract introduces no free parameters, axioms, or invented entities.

pith-pipeline@v0.9.0 · 5476 in / 1057 out tokens · 56522 ms · 2026-05-14T18:48:12.605293+00:00 · methodology

discussion (0)

Lean theorems connected to this paper

Citations machine-checked in the Pith Canon. Every link opens the source theorem in the public Lean library.

IndisputableMonolith/Cost/FunctionalEquation.lean washburn_uniqueness_aczel unclear

?

unclear
Relation between the paper passage and the cited Recognition theorem.

Nonreciprocity in our JJs is induced by the self-field effect... via the second London equation... sine-Gordon model (Eq. 7)
IndisputableMonolith/Foundation/RealityFromDistinction.lean reality_from_one_distinction unclear

?

unclear
Relation between the paper passage and the cited Recognition theorem.

The condition for achieving maximum nonreciprocity is Φ_sf = L_sf I_c0 = Φ_0... short-junction limit W_x < 4 λ_J

What do these tags mean?

matches: The paper's claim is directly supported by a theorem in the formal canon.
supports: The theorem supports part of the paper's argument, but the paper may add assumptions or extra steps.
extends: The paper goes beyond the formal theorem; the theorem is a base layer rather than the whole result.
uses: The paper appears to rely on the theorem as machinery.
contradicts: The paper's claim conflicts with a theorem or certificate in the canon.
unclear: Pith found a possible connection, but the passage is too broad, indirect, or ambiguous to say the theorem truly supports the claim.

Reference graph

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