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Researchers developed a pulsed current measurement technique to study the superconducting gap in bismuth dihydride (BiH₂) at extreme pressures of 157-176 GPa. BiH₂ exhibits superconductivity at 58-70 K with critical magnetic fields of 11-17 T, and measurements of critical current density down to 2 K revealed two-scale energy gaps of approximately 6.9 and 1.5 meV. Theoretical calculations suggest this two-gap behavior likely arises from anisotropy in a single gap rather than two distinct gaps, establishing pulsed current measurements as a viable method for probing superconducting properties under extreme pressure conditions.
Why it matters
This work provides a new experimental approach to characterize high-pressure hydride superconductors, which are candidates for achieving room-temperature superconductivity. The technique could enable future investigations of more exotic hydrides like La-Sc-H that may operate at even higher temperatures, advancing the quest for practical room-temperature superconductors.
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⚠️ Preprint – Noch nicht peer-reviewed
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Abstract: Hydride superconductors at megabar pressures provide a promising platform for exploring room-temperature superconductivity. However, their superconducting gaps remain largely inaccessible to conventional spectroscopic due to diamond anvil cell constraints and minute sample dimensions. Here we develop a pulsed current method and apply it to covalent BiH$_2$ synthesized at 157–176 GPa. BiH$_2$ exhibits superconductivity at 58–70 K and upper critical fields of 11–17 T, substantially lower than those of many clathrate superhydrides, corresponding to a relatively long coherence length and an experimentally accessible critical current density. Short rectangular pulses minimize sustained Joule heating and enable currents up to 160 mA, allowing $J_c(T)$ to be measured in the low-temperature regime down to 2 K at 176 GPa. The normalized critical-current response remains reproducible between two measurement runs and is better described by a two-scale $s$-wave model than by single-gap $s$- or $d$-wave models, yielding effective energy scales of approximately 6.9 and 1.5 meV. Fully anisotropic Migdal–Eliashberg calculations yield a single highly anisotropic gap, suggesting that the two-gap behavior observed experimentally originates from gap anisotropy rather than two independent gaps. These results establish pulsed critical-current measurements as a practical gap-sensitive transport probe under extreme pressure and, with further increases in peak-current capability, provide a route toward investigating room-temperature hydrides such as La–Sc–H.
Source: Superconducting gap in covalent bismuth dihydride BiH$_2$ under extreme conditions