Metallic sulphur. "Electronic" mechanism of superconductivity?

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).