The possible role of van Hove singularities in the high $T_c$ of superconducting H${}_3$S

Abstract

We observe that H${}_3$S has a bcc structure and, with nearest neighbour hopping only, a strong singularity occurs at zero energy. This singularity is accompanied with a highly nested Fermi surface, which is {\it not} conducive to a stable superconducting instability. Introduction of next-nearest-neighbour hopping removes the singularity, but a `robust' peak remains in the electron density of states. Solution of the BCS equations shows an enhanced superconducting $T_c$ due to this peak. Furthermore, nesting is no longer present, so other instabilities will not compete effectively with superconductivity. We find high critical temperatures are possible, even with very modest coupling strengths. We also examine a limit of the $T=0$ equations (in an Appendix) where an analytical solution is possible over the entire range of coupling strengths, and therefore the BCS-BEC crossover is fully covered.

5 pages 2 figures

References in corpus (4)

• Hydrogen sulphide at high pressure: a strongly-anharmonic phonon-mediated superconductor
• Pressure-induced decomposition of solid hydrogen sulfide
• Cubic H${}_3$S around 200 GPa: an atomic hydrogen superconductor stabilized by sulfur
• Hole superconductivity in $H_{2}S$ and other sulfides under high pressure

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• Illuminating the Bragg intersections as roots of Dirac nodal lines and high-order van Hove singularities