On estimating the superconducting volume fraction from the intrinsic magnetic susceptibility data measured in highly compressed Ruddlesden–Popper nickelates

High-temperature superconductivity (HTS) in pressurized Ruddlesden–Popper (RP) nickelates Lan +1NinO3n +1 (n = 2, 3, 4), as well as the superconducting state with zero resistance at Tc, zero ≈10 K in ambient pressure thin films (La, Pr)n +1NinO3n+1 (n = 2), are two new windows to understand the phenomenon of HTS in metal oxides. The detection of the DC diamagnetic state in RP nickelates was a challenging experimental problem until several research groups reported DC zero-field cooled (ZFC) and field cooled (FC) data in the last year. For instance, ZFC and FC measurements in a highly compressed Pr4Ni3O10 single crystal provide unambiguous confirmation of bulk superconductivity in pressurized RP nickelates. To analyse ZFC and FC data many research groups applied an equation to recalculate ZFC data in volume fraction f of the superconducting phase in the sample. In result, f = 0.85 was reported for Pr4Ni3O10 single crystal at pressure P = 40.2 GPa. The key postulate of the methodology for the calculation of f is that f is equal to the amplitude of the intrinsic magnetic susceptibility |χinternal|, or f = |χinternal|. Here we argue that this postulate is incorrect and present counterexample where the Pr4Ni3O10 sample can exhibit f < 0.10 and |χintrinsic| > 0.80. Considering that the postulate f = |χintrinsic| is widely used in superconductivity, we extend our request to reconsider the validity of this postulate in the entire field of superconductivity.

1. Ministry of Science and Higher Education of the Russian Federation - IMP UB RAS