Crystal structures and superconductivity of carbonaceous sulfur hydrides at pressures up to 300 GPa
Ying Sun, Xue Li, Toshiaki Iitaka, Hanyu Liu, Yu Xie
Abstract
To explore the crystal structure of the recently claimed room-temperature superconducting carbonaceous sulfur hydrides, we searched for $\ensuremath{\approx}250\phantom{\rule{0.16em}{0ex}}000$ structures over $\ensuremath{\approx}800$ stoichiometries at 300 GPa via advanced crystal structure searching and cluster expansion method. Only several metastable high-temperature superconductors were identified, whose structures can be classified into hydrogen-rich molecular crystals and low-level carbon-doped ${\mathrm{H}}_{3}\mathrm{S}$-like structures by constructing the ternary phase diagram and simulating the electron-phonon interactions. The C--S--H molecular crystals are composed of ${\mathrm{CH}}_{4}, {\mathrm{SH}}_{6}$, and ${\mathrm{H}}_{2}$ molecules, where the superconductivity (with the highest superconducting critical temperature ${T}_{c}$ is 156 K found in ${\mathrm{CSH}}_{48}$ at 300 GPa) is mainly contributed to by ${\mathrm{H}}_{2}$ units, implying their ${T}_{c}$ values are unlikely to be higher than that of metallic molecular hydrogen (${T}_{c}$ of 242 K at 450 GPa). The highest ${T}_{c}$ of low-level carbon-doped C--S--H compounds (up to 64 atoms in the primitive cell) at 300 GPa was estimated as 189 K for ${\mathrm{H}}_{3}{\mathrm{S}}_{0.917}{\mathrm{C}}_{0.083}$. Our results provide a comprehensive map between the crystal structure and superconductivity of carbonaceous sulfur hydride materials at high pressures.