Recently, it has been reported that room-temperature superconducticity with Tc ~ 280 K emerges in cabonaceous sulfur hydride (C-S-H) systems under high pressure up to 270 GPa . Since their atomic configuration is still not determined, we explore a variety of crystal structures in a C-S-H convex hull and discuss the stability of candidate structures of C-S-H ternary compounds .
Meanwhile, based on ab initio calculations using the McMillan-Allen-Dynes formula, it has been recently shown that carbon-doped H3S with a doping level of around 5% could be a promising candidate for the room-temperature superconductor [3,4]. While the McMillan-Allen-Dynes is based on the constant DOS approximation, in this work we perform ab initio Migdal-Eliashberg calculation considering the significant energy dependence of the van Hove singulartiy around the Fermi level .
Our conclusions include (i) the absence of a dominant low-enthalpy stoichiometry and crystal structure in the ternary phase diagram. (ii) Only the thermodynamics of C-doping phases appears to be marginally competing in enthalpy against H3S. (iii) Accurate results of the transition temperature given by ab initio Migdal-Eliashberg calculations differ by more than 110K from recent theoretical claims explaining the room-temperature superconductivitiy in carbonaceous hydrogen sulfide. An unconventional mechanims of superconductivity or a breakdown of current theories in this system is possibly behind the disagreement.
Fig. 1. C-S-H convex hull of the formation enthalpy calculated for selected stoichiometries at 250 GPa. Different stoichiometries are colored according to their formation enthalpy.
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Keywords: room-temperature superconductivity, hydride superconductors, pressure effects, dopants