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arxiv: 2604.25843 · v1 · submitted 2026-04-28 · ❄️ cond-mat.supr-con · cond-mat.mtrl-sci

Recognition: unknown

Bragg-Williams order competes with superconductivity

Boqin Song, Chuizhen Chen, Dongliang Yang, Feng Jin, Gefei Li, Jian-gang Guo, Jiangping Hu, Jing Chen, Pengju Zhang, Qinghua Zhang, Tianping Ying, Weiwei Dong, Xiaolong Chen, Xijing Dai, Xingya Wang, Xu Chen, Xu Liu

Pith reviewed 2026-05-07 14:34 UTC · model grok-4.3

classification ❄️ cond-mat.supr-con cond-mat.mtrl-sci
keywords Bragg-Williams ordersuperconductivityIn2/3PSe3electron-phonon interactioncompeting ordersvacancy orderingpressure-induced superconductivitystructural order parameter
0
0 comments X

The pith

Bragg-Williams order of indium vacancies suppresses superconductivity by weakening electron-phonon coupling.

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

The paper demonstrates that indium vacancies in In2/3PSe3 can be switched reversibly between ordered and disordered Bragg-Williams configurations solely by thermal treatment. The disordered state reaches a pressure-induced superconducting transition temperature of 11 K, while the ordered state reaches only 7 K. Analysis combining Ginzburg-Landau phenomenology with BCS-McMillan theory shows that the ordered arrangement reduces electron-phonon interaction strength, directly lowering Tc. This provides a clean separation of structural order from charge doping or magnetic effects, allowing readers to see how a classical alloy-order parameter can compete with superconductivity on its own.

Core claim

In In2/3PSe3, indium vacancies are reversibly configurable between Bragg-Williams ordered and disordered states via thermal treatment. The disordered phase undergoes a pressure-induced superconducting transition with Tc of 11 K, higher than the 7 K of the ordered phase. Ginzburg-Landau and BCS-McMillan analysis establishes that Bragg-Williams order suppresses superconductivity through electron-phonon interactions, supported by ultra-low-wavenumber Raman measurements.

What carries the argument

Bragg-Williams order of indium vacancies, functioning as an independent structural order parameter that reduces electron-phonon coupling strength to compete with superconductivity.

If this is right

  • Bragg-Williams order can serve as a reversible tuning parameter for Tc without altering doping.
  • Electron-phonon coupling is the dominant channel through which this structural order affects superconductivity.
  • Competing-order frameworks must incorporate classical structural parameters in addition to electronic and magnetic ones.
  • Thermal annealing protocols offer a route to control superconducting properties in vacancy-containing compounds.

Where Pith is reading between the lines

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

  • Similar vacancy-order tuning may appear in other layered chalcogenides or alloys where annealing can toggle site occupancy.
  • Device concepts could exploit thermal cycling to switch between superconducting and normal states in related materials.
  • The mechanism suggests testing whether other structural orders, such as site-disorder in different lattices, produce comparable Tc suppression.

Load-bearing premise

Thermal treatment alters only the Bragg-Williams ordering of vacancies and introduces no uncontrolled changes in carrier density or additional defects.

What would settle it

Preparing samples with identical carrier density but deliberately varied vacancy order and finding no Tc difference would falsify the claim that Bragg-Williams order alone drives the observed shift.

Figures

Figures reproduced from arXiv: 2604.25843 by Boqin Song, Chuizhen Chen, Dongliang Yang, Feng Jin, Gefei Li, Jian-gang Guo, Jiangping Hu, Jing Chen, Pengju Zhang, Qinghua Zhang, Tianping Ying, Weiwei Dong, Xiaolong Chen, Xijing Dai, Xingya Wang, Xu Chen, Xu Liu.

Figure 1
Figure 1. Figure 1: FIG 1 view at source ↗
read the original abstract

Orderings in charge and spin have been extensively studied to unravel their correlation to emergent superconductivity over the past decades. Bragg-Williams order (BWO), a classical structural order parameter describing site occupancy in alloys, has long been speculated to influence superconducting behavior. Yet, its role still remains ambiguous, largely due to the difficulty of isolating BWO from concomitant charge doping or competing electronic instabilities. Here, we establish In2/3PSe3 as a platform wherein indium vacancies are reversibly configurable between ordered and disordered states via thermal treatment. We show that the disordered phase undergoes a pressure-induced superconducting transition with a Tc of 11 K, significantly higher than the 7 K observed in its ordered counterpart. This constitutes a rare instance in which pure BWO variation drives a substantial shift in Tc. By combining a Ginzburg-Landau phenomenological analysis with a BCS-McMillan microscopic description, we demonstrate that BWO naturally suppresses superconductivity through electron-phonon interactions, a mechanism supported by ultra-low-wavenumber Raman measurements. Our findings support BWO as an independent order parameter that competes directly with superconductivity, extending the concept of competing orders beyond conventional electronic and magnetic degrees of freedom.

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 / 1 minor

Summary. The manuscript claims that In2/3PSe3 serves as a platform where indium vacancies can be reversibly switched between ordered and disordered Bragg-Williams order (BWO) states via thermal treatment. The disordered phase shows a pressure-induced superconducting Tc of 11 K, substantially higher than the 7 K in the ordered phase. Combining Ginzburg-Landau phenomenological analysis with a BCS-McMillan microscopic model, the authors argue that BWO competes with superconductivity by suppressing it through electron-phonon interactions, with supporting evidence from ultra-low-wavenumber Raman measurements. This is positioned as a rare demonstration of pure BWO variation driving a large Tc shift.

Significance. If the experimental controls confirm isolation of the BWO effect, the work offers a valuable new platform for investigating structural order as an independent competing order parameter in superconductors, extending beyond conventional charge, spin, or orbital degrees of freedom. The dual use of Ginzburg-Landau and BCS-McMillan frameworks, together with Raman data, provides a coherent theoretical and experimental link between BWO and the observed Tc difference.

major comments (2)
  1. [Abstract and experimental characterization sections] Abstract and experimental characterization sections: The headline claim requires that the observed ΔTc arises solely from BWO variation. No post-anneal quantitative controls (Hall coefficient for carrier density, EDX for stoichiometry, or high-resolution XRD for lattice parameters) are referenced to bound possible changes in carrier density or additional defects that would also modulate Tc via the same electron-phonon channel used in the BCS-McMillan analysis.
  2. [BCS-McMillan microscopic description] BCS-McMillan microscopic description: The demonstration that BWO 'naturally suppresses superconductivity through electron-phonon interactions' relies on the McMillan formula. It is unclear whether the electron-phonon coupling strength or density of states are independently determined (e.g., from specific-heat or tunneling data) or adjusted to reproduce the 4 K Tc difference; if the latter, the suppression is by construction rather than an independent prediction.
minor comments (1)
  1. [Raman measurements] The ultra-low-wavenumber Raman data are invoked to support the electron-phonon mechanism, but the manuscript should quantify how the observed mode shifts or intensities map onto a change in the McMillan λ parameter between the two BWO states.

Simulated Author's Rebuttal

2 responses · 0 unresolved

We thank the referee for their careful reading of the manuscript and for the constructive comments, which help to clarify the isolation of the Bragg-Williams order effect. We address each major comment below and indicate the revisions that will be incorporated.

read point-by-point responses

  1. Referee: [Abstract and experimental characterization sections] Abstract and experimental characterization sections: The headline claim requires that the observed ΔTc arises solely from BWO variation. No post-anneal quantitative controls (Hall coefficient for carrier density, EDX for stoichiometry, or high-resolution XRD for lattice parameters) are referenced to bound possible changes in carrier density or additional defects that would also modulate Tc via the same electron-phonon channel used in the BCS-McMillan analysis.

    Authors: We agree that post-anneal quantitative controls would strengthen the isolation of the BWO effect. In the revised manuscript we will add Hall coefficient data measured after the thermal treatments to bound carrier-density variations, together with a discussion of the existing EDX and high-resolution XRD results that confirm stoichiometry and lattice parameters remain essentially unchanged between the ordered and disordered phases. The reversible switching protocol and the distinct ultra-low-wavenumber Raman signatures already indicate that the dominant difference is vacancy ordering rather than doping or additional defects; the added controls will make this explicit. revision: partial

  2. Referee: [BCS-McMillan microscopic description] BCS-McMillan microscopic description: The demonstration that BWO 'naturally suppresses superconductivity through electron-phonon interactions' relies on the McMillan formula. It is unclear whether the electron-phonon coupling strength or density of states are independently determined (e.g., from specific-heat or tunneling data) or adjusted to reproduce the 4 K Tc difference; if the latter, the suppression is by construction rather than an independent prediction.

    Authors: The McMillan parameters are not adjusted to fit the observed Tc values. The change in electron-phonon coupling is estimated directly from the softening and broadening of the ultra-low-wavenumber Raman modes that are sensitive to the indium-vacancy ordering, while the density of states is obtained from the structural model of the ordered versus disordered phases. These inputs, together with the Ginzburg-Landau analysis, yield the predicted Tc shift without free fitting to the experimental transition temperatures. The revised manuscript will include an expanded methods section that tabulates the Raman-derived parameters and shows the step-by-step calculation to make the independence of the prediction clear. revision: yes

Circularity Check

0 steps flagged

No significant circularity; derivation uses standard frameworks on independent data

full rationale

The paper observes a Tc difference between ordered and disordered In2/3PSe3 phases, then applies the established Ginzburg-Landau and BCS-McMillan formalisms plus Raman data to interpret the role of Bragg-Williams order. No equations or steps are presented that reduce a claimed prediction back to a fitted parameter or self-citation by construction. The frameworks are external and the supporting measurements (Raman, thermal treatment effects) are described as independent of the target Tc attribution, keeping the chain self-contained against external benchmarks.

Axiom & Free-Parameter Ledger

1 free parameters · 2 axioms · 0 invented entities

The central claim rests on the assumption that thermal treatment affects only site occupancy order and that standard phenomenological theories can be applied without additional fitted parameters specific to this material. No new particles or forces are postulated.

free parameters (1)
  • electron-phonon coupling strength or related McMillan parameters
    Likely adjusted within the BCS-McMillan description to reproduce the observed Tc difference between ordered and disordered phases.
axioms (2)
  • domain assumption Ginzburg-Landau theory applies to the competition between BWO and superconductivity
    Invoked in the phenomenological analysis section of the abstract.
  • domain assumption BCS-McMillan framework correctly captures the suppression mechanism through electron-phonon interactions
    Used to link BWO to Tc shift; standard in superconductivity but assumes the dominant pairing channel.

pith-pipeline@v0.9.0 · 5560 in / 1576 out tokens · 103139 ms · 2026-05-07T14:34:49.199997+00:00 · methodology

discussion (0)

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Reference graph

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