Comment on "Conventional superconductivity at 203 kelvin at high pressures in the sulfur hydride system" (A. P. Drozdov et al., Nature 525, 73 (2015))

Abstract

It is demonstrated that resistive transition at 203 K observed in metallic sulfur hydride system at high pressure can be magnetic (rather than superconducting (SC)) in nature. The onset temperature of genuine superconducting transition in these compounds appears to be essentially lower on temperature. The normal-state magnetic (AF SDW) phase transition preceding a superconducting one (Tc < Tm) is characteristic for HTSC cuprates, pnictides (selenides) and organic superconductors. The resistive drop is provided by disappearing of magnetic (AF spin fluctuation) scattering of conduction electrons and hence formation of AF SDW order in the normal state. The formation of such modulated magnetic structure in sulfur hydride seems to be possible because of magnetic properties of metallic hydrogen at high densities (in analogy with iron). Such unconventional picture with two successive phase transitions: magnetic (AF SDW) and only then superconducting one is naturally described by Keldysh-Kopaev theory of dielectric (metal-insulator) phase transition in systems with coexistence of superconducting (e-e) and dielectric (e-h)pairings.