Metallic sulphur. "Electronic" mechanism of superconductivity?

TL;DR

The paper discusses how the increase in sulfur's superconducting transition temperature under high pressure supports an electronic mechanism of superconductivity, with implications for high $T_c$ and bond type transitions.

Contribution

It proposes that sulfur's high-pressure superconductivity can be explained by an intrinsic electronic mechanism involving electron interaction energy fluctuations.

Findings

Superconducting $T_c$ increases rapidly above 93 GPa.

The electronic mechanism may account for very high $T_c$ in molecular condensates.

Bond type transitions under pressure can cause $T_c$ to have an extremum.

Abstract

It is shown that the rapid increase of the superconducting transition temperature $T_c$ of sulphur with increasing pressure above 93 GPa does not contradict with some hypothetical ``electronic'' mechanism of superconductivity with participation of the electron interaction energy fluctuations. Such ``electronic'' mechanism is supposed to be intrinsic property of the molecular condensates and corresponds to very high $T_c$. The low $T_c$ of sulphur (10 -17)K is likely connected with the magnetic properties of the sulphur atoms and molecules. The equation of state for sulphur is obtained. The molar volume of sulphur at metallization is 10 cm}$^3${/mol. The principal difference between the ''physical'' and the ''chemical'' type bonds are discussed. Under some pressure one bond type is changed by another and}${T}_c${may have an extremum (transition from the Bose condensation to the BCS superconductivity).