Van Hove singularities and spectral smearing in high-temperature superconducting H3S

摘要

The superconducting phase of hydrogen sulfide at T-c = 200 K observed by Drozdov and collaborators at pressures around 200 GPa is simple bcc Im (3) over barm H3S from a combination of theoretical and experimental confirmation. The various "extremes" that are involved-high pressure implying extreme reduction of volume, extremely high H phonon energy scale around 1400 K, extremely high temperature for a superconductor-necessitates a close look at new issues raised by these characteristics in relation to high T-c itself. First principles methods are applied to analyze the H3S electronic structure, beginning with the effect of sulfur and then focusing on the origin and implications of the two van Hove singularities (vHs) providing an impressive peak in the density of states near the Fermi energy. Implications arising from strong coupling Migdal-Eliashberg theory are studied. It becomes evident that electron spectral density smearing due to virtual phonon emission and absorption must be accounted for in a correct understanding of this unusual material and to obtain accurate theoretical predictions. Means for increasing T-c in H3S-like materials are noted.