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

Abstract

Zhang et al.${}^1$ reported zero-field cooled (ZFC) and field cooled (FC) data measured in a highly compressed $P{r}_{4}N{i}_3{O}_{10}$ single crystal. These measurements provide unambiguous confirmation of bulk superconductivity in pressurized Ruddlesden-Popper nickelates. Zhang et al.${}^1$ applied an equation (described in Refs.${}^{2,3}$) to recalculate ZFC data measured in a $P{r}_{4}N{i}_3{O}_{10}$ (sample S3) in volume fraction $f$ of the superconducting phase in the sample. In result${}^1$, $f=0.85$ was reported for sample S3 at pressure P = 40.2 GPa. The key postulate of the methodology for the calculation of $f$ (see also works${}^{4-6}$) is that $f$ is equal to the amplitude of the internal magnetic susceptibility $|{\chi }_{internal}|$, or $f=|{\chi }_{internal}|$. Here we argue that this postulate is incorrect and present counterexample where the $P{r}_{4}N{i}_3{O}_{10}$ sample S3 can exhibit $f<0.10$ and $|{\chi }_{internal}|=0.82$. In the result, we addressed recent Replies${}^{2,3}$ on our Comments${}^{7,8}$. Considering that the postulate $f=|{\chi }_{internal}|$ is widely used in superconductivity, we extend our request to reconsider the validity of this postulate in the entire field of superconductivity.

arXiv comment11 pages, 1 figure