Nearly twofold overestimation of the superconducting volume fraction in pressurized Ruddlesden-Popper nickelates

TL;DR

This paper identifies a significant overestimation in the reported superconducting volume fraction in pressurized Ruddlesden-Popper nickelates due to an incorrect calculation method, affecting previous experimental conclusions.

Contribution

The authors reveal that the standard procedure and equation used to calculate the superconducting volume fraction are incorrect, leading to overestimations in prior studies.

Findings

Reported volume fractions are overestimated by nearly twofold.

The standard calculation method is flawed and results in inflated superconducting volume estimates.

Previous experimental claims of high superconducting volume fractions need reassessment.

Abstract

The detection of the DC diamagnetic state in pressurized Ruddlesden-Popper nickelates remained an unsolved experimental problem until recent experiments in which Zhu et al.$^1$ measured the DC diamagnetic responses in zero-field cooled (ZFC) mode in pressurized La4Ni3O10. Zhu et al.$^1$ reported that the ratio of the measured ZFC magnetic moment to the Meissner magnetic moment of the sample (and this ratio was termed the superconducting volume fraction$f$) reaches 81-86%. We regard outstanding experimental results$^1$; however, our calculations based on the reported experimental datasets$^1$ using the standard procedure showed the ratio to be 51-59%. Upon our request, Zhu et al.$^1$ provided detailed explanations and the equation they used to calculate$f$. To our knowledge, the procedure$^1$ and equation$^1$ for calculating $f$ have never been mentioned or described before, including in Ref.$^1$. Here we argue that the proposed equation$^1$ and procedure$^1$ are incorrect, and that this equation$^1$ results in multiple overestimations of the superconducting volume fraction in the sample. This overestimation error affects all superconducting volume fractions $f$ in Ruddlesden-Popper nickelates reported to date$^{1-4}$. Therefore, we describe the error we discovered in this paper.