Intrinsic hysteresis in the presumed superconducting transition of hydrides under high pressure

TL;DR

This paper investigates the intrinsic hysteresis observed in resistance drops of hydrides under high pressure, questioning whether these are genuine superconducting transitions or artifacts, and concludes they may not be superconductors.

Contribution

It provides evidence that the hysteresis in hydrides is intrinsic and suggests these materials may not be superconductors, challenging previous interpretations.

Findings

Hysteresis is intrinsic to the samples, not an experimental artifact.

The resistance drops likely indicate first order phase transitions.

Superhydrides may not be superconductors, contrary to prior assumptions.

Abstract

Superconducting transitions in the absence of magnetic field should be non-hysteretic. Here we address the fact that the drops in electrical resistance that have been interpreted as evidence of superconductivity in several hydrides under high pressure (so-called "superhydrides") show hysteresis. We argue that the experimental evidence shows that the observed hysteresis cannot be attributed to experimental artifacts but is intrinsic to the samples. Assuming that the drops in resistance signal a thermodynamic phase transition, we argue that the presence of intrinsic thermal hysteresis indicates that these are first order transitions, whereas for standard superconductors the transition in the absence of applied magnetic field is always second order. We conclude that this is another feature that qualitatively distinguishes superhydrides from standard superconductors, in addition to the ones that have been pointed out earlier [1,2], $assuming$ these materials are superconductors. Alternatively and more likely, whether or not the drops in resistance signal a thermodynamic phase transition, our analysis indicates that superhydrides are not superconductors.