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

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.

Paper withdrawn because we received additional information from the authors of Refs.[6] and [8] that supports their statements that the hysteresis is due to lack of thermal equilibration. Also the authors of Ref.[4] informed us that a diamond had cracked on or after the cooling cycle, resulting in an uncontrolled pressure shift that could explain the hysteresis in their Fig.3

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• Superconductivity up to 243 K in yttrium hydrides under high pressure
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• Anomalous behavior in high-pressure carbonaceous sulfur hydride
• Controlling Metal-Insulator Transitions in Vanadium Oxide Thin Films by Modifying Oxygen Stoichiometry
• Thermodynamics around the First-Order Ferromagnetic Phase Transition of ${\mathrm{Fe}}_2\mathrm{P}$ Single Crystals
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Cited by in corpus (1)

• High-temperature superconductivity in hydrides: experimental evidence and details