Refined phase diagram of the H-S system with high- Tc superconductivity

Abstract

Recently, hydrogen sulfide has attracted enormous attention due to the record high-temperature superconductivity of ${\text{H}}_{3}\text{S}$ with ${T}_{c}=203$ K at a pressure of 155 GPa. In addition to ${\text{H}}_{3}\text{S}$, there are many theoretically and experimentally confirmed compositions and crystal structures forming under high pressure. Here, using the ab initio variable-composition evolutionary algorithm USPEX, we performed a comprehensive search for new phases in the $\text{H}\ensuremath{-}\text{S}$ system and built a refined composition-pressure phase diagram. For ${\text{H}}_{3}{\text{S}}_{2}$, a new stable semiconducting $P{2}_{1}$ phase was found. We predicted a new sulfur-rich stable ${\text{HS}}_{2}$ phase and metastable compound ${\text{H}}_{5}{\text{S}}_{8}$ and calculated their ${T}_{c}$ using superconducting density functional theory (11 K at 100 GPa and 9.2 K at 80 GPa, respectively). Our results show that among stable phases only ${\text{H}}_{3}\text{S}$ is a high-${T}_{c}$ superconductor, and highlight that compositional descriptors alone are insufficient for indicating superconductivity, and crystal structure plays an essential role.