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

Summary

Zhang et al. [1] reported zero-field cooling (ZFC) and field cooling (FC) data for Pr₄Ni₃O₁₀ single crystals under high pressure, confirming bulk superconductivity in Ruddlesden-Popper nickelates and estimating a superconducting volume fraction f = 0.85 using the amplitude of the internal susceptibility χ_internal. This paper questions the key assumption of that method, namely f = |χ_internal|, and demonstrates through a counterexample that even when the calculated |χ_internal| for a sample reaches 0.82, the actual superconducting volume fraction f may be below 0.10. The authors point out that 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—if 90.2% 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. Therefore, χ_internal alone cannot uniquely determine f, and this approach requires reexamination across the entire field of superconductivity research.

Materials

• Pr₄Ni₃O₁₀
• La₂SmNi₂O₇

Methods

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

Keywords

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

Highlights

• 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.

Conclusions

• 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.

Main claims

• The postulate that f = |χ_internal| (superconducting volume fraction equals internal susceptibility amplitude) is incorrect.
  • Evidence: 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.
  • Evidence: 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.
  • Evidence: 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'

Workflow

Not available in this batch.