Revaluation of the lower critical field in superconducting H$_3$S and LaH$_{10}$ (Nature Comm. 13, 3194, 2022)

TL;DR

This study re-evaluates the lower critical magnetic field in superconducting hydrides H$_3$S and LaH$_{10}$ using improved data analysis methods to address previous criticisms, confirming their superconducting properties.

Contribution

The paper introduces an alternative data analysis approach for estimating the lower critical field Hp that avoids data smoothing, validating the superconductivity in hydrides despite prior methodological criticisms.

Findings

Consistent Hp values with original analysis

Superconducting hysteresis observed below Tc

Validation of hydride superconductivity

Abstract

In our paper [1], we studied the magnetic response of H$_3$S and LaH$_{10}$ superconductors to an applied magnetic field using Superconducting Quantum Interference Device (SQUID) magnetometry. Hirsch, in his comment [2], highlighted an inconsistency in the data averaging procedure while questioning whether high-Tc hydrides are superconductors at all. We accept the criticism regarding our method of extracting the penetration field HP from the original data. Our SQUID magnet becomes noisy at high magnetic fields, which necessitated the smoothing of a small portion of the data. To eliminate any data processing issues, we have performed an alternative data analysis that does not require data smoothing to estimate the penetration field Hp values. The formulation of the analysis is identical to the one widely used for determining critical currents in superconductors3. Recently, it has been shown to work effectively for extracting Hp and the lower critical field Hc1 from DC magnetization data4. The Hp values of the present analysis are consistent with those published in our original work1. We wish to emphasize very clearly that the criticism pertains to the secondary issue of determining Ginzburg-Landau parameters for these hydride superconductors and does not undermine the validity of the existence of hydride superconductivity. Indeed, as part of our paper1, we also published m(H) curves demonstrating the virgin curve (about which the analysis issues were raised) followed by magnetic hysteretic loops that have the classic form of the hysteresis curves of superconductors. Above Tc, in both H$_3$S and LaH$_{10}$, the hysteresis is absent. We make all the data available so that readers can judge for themselves.