# On Trapped Flux in a Small Crystal of CaKFe4As4 and Implications for High-Pressure Hydrides

## TL;DR

This paper discusses trapped magnetic flux in a superconducting crystal and its relevance to interpreting superconductivity in high-pressure hydrides.

## Contribution

The paper challenges the interpretation of trapped flux measurements in high-pressure hydrides as evidence for superconductivity.

## Key findings

- Trapped flux measurements in CaKFe4As4 support alternative interpretations of similar data in hydrides.
- The results suggest that observed trapped flux may not be consistent with superconductivity in high-pressure hydrides.

## Abstract

In recent work (Bud’ko et al. Supercond. Sci. Technol. 37, 065010 2024), Bud’ko et al. present experimental results for trapped magnetic flux for a tiny sample of a type II superconductor, \documentclass[12pt]{minimal}
\usepackage{amsmath}
\usepackage{wasysym}
\usepackage{amsfonts}
\usepackage{amssymb}
\usepackage{amsbsy}
\usepackage{mathrsfs}
\usepackage{upgreek}
\setlength{\oddsidemargin}{-69pt}
\begin{document}$$CaKFe_4As_4$$\end{document}CaKFe4As4. The paper aims to provide evidence in support of the interpretation that similar measurements performed in samples of hydrogen-rich materials under high pressure by Minkov et al. (Nat. Phys. 19, 1293 2023) are conclusive evidence (Eremets Nat. Sci. Rev. 11, nwae047 2024) for superconductivity in hydrides under pressure. Here, we point out that the new evidence presented by Bud’ko et al. (Supercond. Sci. Technol. 37, 065010 2024) further supports our interpretation (Hirsch and Marsiglio J. Supercond. Nov. Magn. 35, 3141–3145 2022; Hirsch and Marsiglio Phys. C 620, 1354500 2024) that the reported measurements of trapped flux on hydrides under pressure (Minkov et al. Nat. Phys. 19, 1293 2023) are not consistent with what would be expected from a superconducting sample.