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arxiv: 2605.10226 · v1 · submitted 2026-05-11 · ❄️ cond-mat.supr-con · cond-mat.stat-mech· cond-mat.str-el

Recognition: 2 theorem links

· Lean Theorem

Apparent double-T_c from a single BKT transition in anisotropic phase-only models

Authors on Pith no claims yet

Pith reviewed 2026-05-12 03:10 UTC · model grok-4.3

classification ❄️ cond-mat.supr-con cond-mat.stat-mechcond-mat.str-el
keywords BKT transitionJosephson junction arrayanisotropic superconductorsdouble transition temperatureresistively shunted junctionfinite-size scalingvortex dynamics
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0 comments X

The pith

Anisotropic phase-only models yield a single BKT transition yet produce apparent double-Tc in linear resistance curves under nonequilibrium dynamics.

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

The paper examines a minimal model of anisotropic Josephson-junction arrays both in equilibrium and driven by resistively shunted junction dynamics with fluctuating twist boundaries. Equilibrium calculations show only one Berezinskii-Kosterlitz-Thouless transition. Out of equilibrium, anisotropy in the couplings and in the dissipation distorts the shape of linear resistance-versus-temperature curves within the finite-size and finite-current crossover window. Methods that rely on curve shape, such as Halperin-Nelson fitting or fixed-resistance thresholds, therefore report two apparent transition temperatures, while scaling-based diagnostics that use the universal exponent of three and dynamic finite-size collapse remain consistent with a single transition. This establishes a clean baseline in which transport artifacts can mimic thermodynamic splitting without any actual second transition.

Core claim

In the equilibrium anisotropic phase-only Josephson-junction array there is a single Berezinskii-Kosterlitz-Thouless transition. When the same array is driven out of equilibrium under resistively shunted junction dynamics with anisotropic dissipation and fluctuating twist boundary conditions, the linear R-T curves in the finite-size finite-current regime are reshaped so that curve-shape criteria indicate an apparent double-Tc, whereas critical-scaling criteria (the exponent alpha equals three together with dynamic finite-size scaling) continue to signal only the single TBKT.

What carries the argument

The minimal anisotropic phase-only Josephson-junction array governed by resistively shunted junction dynamics with fluctuating twist boundary conditions, whose equilibrium state supports a single BKT transition while its nonequilibrium transport is sensitive to anisotropy.

If this is right

  • Curve-shape analyses of linear R-T data can produce misleading reports of multiple transitions in anisotropic systems.
  • Universal scaling criteria remain reliable indicators of a single underlying BKT transition even when linear curves appear split.
  • Any splitting that survives into the nonlinear critical regime lies outside the physics captured by this minimal anisotropic baseline.

Where Pith is reading between the lines

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

  • The baseline can be used to test whether additional ingredients such as amplitude fluctuations or disorder are required to explain experimental reports of persistent double-Tc.
  • Similar anisotropy-induced distortions may appear in other two-dimensional systems whose transport is governed by vortex unbinding.
  • Extending the model to include weak amplitude fluctuations would provide a direct check on whether the apparent double-Tc survives or is altered.

Load-bearing premise

The minimal anisotropic phase-only Josephson-junction array under resistively shunted junction dynamics captures the essential transport physics without amplitude fluctuations or additional microscopic details.

What would settle it

An experiment on an anisotropic two-dimensional superconductor that measures both linear resistance curves and the dynamic finite-size scaling or the exponent alpha equals three; consistency of the scaling diagnostics with a single transition while the curve-shape methods show splitting would support the claim.

Figures

Figures reproduced from arXiv: 2605.10226 by Pei-Yuan Cai, Yi Zhou.

Figure 1
Figure 1. Figure 1: FIG. 1. Schematic of the anisotropic phase-only model and the RSJ [PITH_FULL_IMAGE:figures/full_fig_p002_1.png] view at source ↗
Figure 2
Figure 2. Figure 2: FIG. 2. Geometric-mean helicity modulus divided by tempera [PITH_FULL_IMAGE:figures/full_fig_p005_2.png] view at source ↗
Figure 3
Figure 3. Figure 3: FIG. 3. Dimensionless [PITH_FULL_IMAGE:figures/full_fig_p006_3.png] view at source ↗
Figure 5
Figure 5. Figure 5: FIG. 5. Dynamic finite-size scaling of the [PITH_FULL_IMAGE:figures/full_fig_p007_5.png] view at source ↗
Figure 8
Figure 8. Figure 8: FIG. 8. Zoom-in of low-resistance regions of the normalized linear [PITH_FULL_IMAGE:figures/full_fig_p008_8.png] view at source ↗
Figure 9
Figure 9. Figure 9: FIG. 9. Halperin–Nelson fits of the normalized linear resistance for [PITH_FULL_IMAGE:figures/full_fig_p009_9.png] view at source ↗
Figure 10
Figure 10. Figure 10: FIG. 10. E [PITH_FULL_IMAGE:figures/full_fig_p011_10.png] view at source ↗
Figure 11
Figure 11. Figure 11: FIG. 11. Geometric-mean sti [PITH_FULL_IMAGE:figures/full_fig_p013_11.png] view at source ↗
read the original abstract

Transport experiments on two-dimensional superconductors often yield direction-dependent transition temperatures, raising the question of whether such a ``double-$T_c$'' reflects a true thermodynamic splitting or a transport artifact. To establish a baseline, we study a minimal anisotropic phase-only Josephson-junction array in equilibrium and under resistively shunted junction dynamics with fluctuating twist boundary conditions. The equilibrium model exhibits a single Berezinskii--Kosterlitz--Thouless (BKT) transition. Out of equilibrium, anisotropic Josephson couplings and anisotropic dissipation reshape the linear $R$--$T$ curves in a finite-size, finite-current crossover regime, so that curve-shape criteria such as Halperin--Nelson fits and fixed-resistance thresholds yield an apparent double-$T_c$. In contrast, critical-scaling criteria -- the universal exponent $\alpha=3$ and dynamic finite-size scaling -- remain consistent with the single $T_{\mathrm{BKT}}$. A robust splitting that persists in the nonlinear critical scaling, such as that recently reported at KTaO$_3$ interfaces, therefore points to physics beyond this clean anisotropic baseline.

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

2 major / 2 minor

Summary. The manuscript studies a minimal anisotropic phase-only Josephson-junction array to address whether direction-dependent transition temperatures in 2D superconductors reflect a true thermodynamic double-Tc or a transport artifact. Equilibrium simulations establish a single Berezinskii-Kosterlitz-Thouless (BKT) transition. Under resistively shunted junction dynamics with anisotropic Josephson couplings, anisotropic dissipation, and fluctuating twist boundary conditions, the linear R-T curves are reshaped in the finite-size/finite-current crossover regime such that curve-shape criteria (Halperin-Nelson fits, fixed-resistance thresholds) produce an apparent double-Tc, while critical-scaling criteria (universal exponent α=3 and dynamic finite-size scaling) remain consistent with a single TBKT. The work concludes that any splitting persisting into nonlinear scaling (as reported at KTaO3 interfaces) requires physics beyond this clean anisotropic baseline.

Significance. If the results hold, the paper supplies a useful parameter-free baseline for interpreting anisotropic 2D superconductor transport data. It cleanly separates apparent effects arising from anisotropy in the crossover regime from true thermodynamic splitting, using only standard Josephson-array and BKT ingredients. The explicit demonstration that universal scaling criteria survive while curve-shape criteria do not is of direct experimental relevance. Credit is given for the absence of free parameters or ad-hoc axioms and for combining equilibrium and dynamical simulations.

major comments (2)
  1. [Dynamical simulations and scaling analysis] The central distinction between curve-shape and scaling criteria is load-bearing. The dynamical simulations section should quantify the finite-size crossover more explicitly: state the linear sizes L simulated, the current densities employed, and the precise metric used to demarcate the crossover regime so that readers can verify that the reported α=3 and dynamic FSS analyses are performed outside that regime.
  2. [Model definition and limitations] The phase-only truncation is the model's defining approximation. While the manuscript correctly presents the result as a baseline, the discussion should briefly address whether amplitude fluctuations (omitted here) could renormalize the effective anisotropy or modify the I-V exponent near TBKT, citing relevant literature on amplitude-inclusive anisotropic models.
minor comments (2)
  1. [Notation] Notation for the BKT temperature is inconsistent (T_BKT vs. T_{BKT}); adopt a single form throughout text and figures.
  2. [Figures] Figure captions for R-T and scaling plots should explicitly state the anisotropy ratios (J_x/J_y and dissipation anisotropy) used in each panel.

Simulated Author's Rebuttal

2 responses · 0 unresolved

We thank the referee for the positive assessment of our manuscript and for the constructive suggestions. We address each major comment below and will revise the manuscript accordingly to improve clarity.

read point-by-point responses
  1. Referee: [Dynamical simulations and scaling analysis] The central distinction between curve-shape and scaling criteria is load-bearing. The dynamical simulations section should quantify the finite-size crossover more explicitly: state the linear sizes L simulated, the current densities employed, and the precise metric used to demarcate the crossover regime so that readers can verify that the reported α=3 and dynamic FSS analyses are performed outside that regime.

    Authors: We agree that explicitly quantifying the finite-size crossover will strengthen the manuscript and help readers verify the separation between curve-shape and scaling criteria. In the revised version, we will add a dedicated paragraph in the dynamical simulations section that states the linear sizes L simulated, the current densities employed, and the precise metric (e.g., the temperature window in which the linear resistance deviates from the Halperin-Nelson form or where finite-size effects begin to dominate) used to demarcate the crossover regime. We will also explicitly confirm that the α=3 exponent and dynamic finite-size scaling analyses are performed outside this regime, where the scaling is robust. This addition will allow readers to independently assess the distinction. revision: yes

  2. Referee: [Model definition and limitations] The phase-only truncation is the model's defining approximation. While the manuscript correctly presents the result as a baseline, the discussion should briefly address whether amplitude fluctuations (omitted here) could renormalize the effective anisotropy or modify the I-V exponent near TBKT, citing relevant literature on amplitude-inclusive anisotropic models.

    Authors: We agree that a brief discussion of the phase-only approximation is appropriate to contextualize the baseline nature of our results. In the revised manuscript, we will add a short paragraph (in the model section or conclusions) noting that amplitude fluctuations, while omitted here, could in principle renormalize the effective anisotropy ratio in certain regimes. However, near TBKT in clean 2D systems, the I-V exponent remains close to the universal value according to existing studies. We will cite relevant literature on amplitude-inclusive anisotropic models (e.g., works extending the XY model to include amplitude dynamics and anisotropic Ginzburg-Landau simulations) to support this point. This will reinforce that any experimentally observed splitting persisting into the nonlinear scaling regime requires physics beyond the clean anisotropic phase-only baseline. revision: yes

Circularity Check

0 steps flagged

No significant circularity; results follow from explicit simulation of a standard phase-only model

full rationale

The paper defines a minimal anisotropic Josephson-junction array from standard BKT and RSJ ingredients, then reports numerical results for equilibrium (single BKT) and driven transport (apparent double-Tc only in curve-shape criteria). No equations reduce a claimed prediction to a fitted input by construction, no load-bearing self-citation chain is invoked to establish the single-TBKT premise, and no ansatz is smuggled via prior work. The central distinction between criteria is obtained directly from the model's dynamics rather than by renaming or self-definition.

Axiom & Free-Parameter Ledger

0 free parameters · 2 axioms · 0 invented entities

The central claim rests on the phase-only approximation and the validity of resistively shunted junction dynamics for capturing transport in the anisotropic case. No new entities are introduced.

axioms (2)
  • domain assumption Phase-only approximation is valid (amplitude fluctuations negligible).
    Standard assumption in Josephson-junction array models for 2D superconductors near the BKT regime.
  • domain assumption Resistively shunted junction dynamics with fluctuating twist boundary conditions adequately represent out-of-equilibrium transport.
    Invoked to generate the linear R-T curves and finite-current crossover regime.

pith-pipeline@v0.9.0 · 5504 in / 1555 out tokens · 53078 ms · 2026-05-12T03:10:34.893976+00:00 · methodology

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Reference graph

Works this paper leans on

54 extracted references · 54 canonical work pages

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