Absence of conventional room-temperature superconductivity at high pressure in carbon-doped H₃S

Recently, it has been reported that room-temperature superconductivity with T_c ~ 280 K emerges in carbonaceous sulfur hydride (C-S-H) system under high pressure up to 270 GPa¹. Since their atomic configuration is still not determined, we explore a variety of crystal srutcutre in a C-S-H convex hull and discuss the stability of candidate structures of C-S-H ternary compounds².

In this work, we show that the same theoretical tools that successfully explain other hydride systems under pressure seem to be at odds with the recently claimed conventional room-temperature superconductivity of carbonaceous sulfur hydride. We support our conclusions with (i) the absence of a dominant low-enthalpy stoichiometry and crystal structure in the ternary phase diagram. (ii) Only the thermodynamics of carbon-doping phases appear to e marginally competing in enthalpy against H3S. (iii) Accurate results of the transition temperature given by ab initio Migdal-Eliashberg calculations³ differ by more than 110 K from recent theoretical claims explaining the high-temperature superconductivity in carbonaceous hydrogen sulfide^4,5. An unconventional mechanism of superconductivity or a breakdown of current theories in this system is possibly behind the disagreement.

¹E. Snider et al., Nature 586, 373-377 (2020)

²T. Wang et al., Phys. Rev. B 104, 064510 (2021)

³T. Wang et al., Phys. Rev. B 102, 134503 (2020)

⁴Y. Ge et al., Materials Today Physics 15, 100330 (2020)

⁵S. X. Hu et al., arXiv:2012.10259