Cubic H$_3$S around 200 GPa: an atomic hydrogen superconductor stabilized by sulfur

TL;DR

This paper applies a multiple scattering theory to analyze Im-3m H3S at high pressure, revealing it as a stabilized atomic hydrogen superconductor with significant anharmonic effects, potentially guiding discovery of new high-temperature superconductors.

Contribution

It introduces a simplified model separating vibrational modes of sulfur and hydrogen, providing insights into the atomic-level mechanisms of high-pressure superconductivity in H3S.

Findings

H3S is a stable phase at around 190 GPa with high-temperature superconductivity.

Superconductivity arises from atomic hydrogen stabilized by covalent mixing with sulfur.

Large anharmonicity in hydrogen vibrations affects isotope shift observations.

Abstract

The multiple scattering-based theory of Gaspari and Gyorffy for the electron-ion matrix element in close packed metals is applied to Im-3m H3S, which has been predicted by Duan {\it et al.} and Bernstein {\it et al} to be the stable phase at this stoichiometry around 190 GPa, thus is the leading candidate to be the phase observed to superconduct at 190K by Drozdov, Eremets, and Troyan. The nearly perfect separation of vibrational modes into those of S and of H character provides a simplification that enables identification of contributions of the two atoms separately. The picture that arises is basically that of superconducting atomic H stabilized by strong covalent mixing with S 3p and "3d" character. The reported isotope shift is much larger than the theoretical one,suggesting there is large anharmonicity in the H vibrations. Given the relative unimportance of sulfur, hydrides of lighter atoms at similarly high pressures may also lead to high temperature superconductivity.