On the estimating the superconducting volume fraction from the internal magnetic susceptibility

摘要

Zhang等人[1]报道了高压下Pr₄Ni₃O₁₀单晶的零场冷却(ZFC)和场冷却(FC)数据，证实了Ruddlesden-Popper镍酸盐中的体超导电性，并利用内部磁化率χ_internal的幅度估算超导体积分数f=0.85。本文对该方法的关键假设f=|χ_internal|提出质疑，并通过反例说明：即使样品计算出的|χ_internal|达0.82，实际超导体积分数f可能低于0.10。作者指出，退磁因子N的计算依赖于非超导区域在样品中的分布，而均匀性假设并不成立——若90.2%的体积为非超导相，只要其几何形状改变退磁因子，磁化率测量值仍可匹配原始结果。因此，仅凭χ_internal无法唯一确定f，该方法在整个超导研究领域需要重新审视。

材料

• Pr₄Ni₃O₁₀
• La₂SmNi₂O₇

方法

• magnetostatic calculations
• demagnetization factor calculation
• analysis of ZFC magnetization data

关键词

• superconducting volume fraction
• internal magnetic susceptibility
• demagnetization factor
• meissner moment
• sample homogeneity assumption
• overestimation

亮点

• The calculation of the demagnetizing factor N depends on the distribution of non-superconducting regions within the sample, and the homogeneity assumption does not hold.
• A counterexample demonstrates that even when the calculated |χ_internal| reaches 0.82, the actual superconducting volume fraction f may be below 0.10.

结论

• The postulate that f = |χ_internal| is incorrect.
• If₉₀.2% of the volume is non-superconducting phase, the measured susceptibility can still match the original results as long as the geometry alters the demagnetizing factor.
• χ_internal alone cannot uniquely determine f, and this approach requires reexamination across the entire field of superconductivity.

主要论断

• The postulate that f = |χ_internal| (superconducting volume fraction equals internal susceptibility amplitude) is incorrect.
  • 证据: abstract: 'we argue that this postulate is incorrect',full_text presents counterexample where calculated |χ_internal| = 0.82 but f < 0.10
• The demagnetization factor N depends on the spatial distribution of non-superconducting regions, so homogeneous assumption does not hold.
  • 证据: full_text: 'a Sample A with 90.2% non-superconducting volume can still yield the same measured moment and χ_internal',abstract: 'if 90.2% of the volume is non-superconducting phase, the measured susceptibility can still match the original results'
• The method of estimating superconducting volume fraction from internal susceptibility needs re-evaluation across the entire field of superconductivity.
  • 证据: abstract: 'we extend our request to reconsider the validity of this postulate in the entire field of superconductivity',full_text: 'we therefore need to call for the re-evaluation of the validity of the postulate'

研究流程

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