Superconductivity determined by the S-H framework in CH4-inserted S-H framework hydrides under high pressures.

Recently, a debate is raising the concern of possible carbonaceous sulfur hydrides with room-temperature superconductivity around 270 GPa. In order to systematically investigate the structural information and relevant natures of C-S-H superconductors, we performed an extremely extensive structure search and first-principles calculations under high pressures. As a result, the metastable stoichiometries of CSH7, C2SH14, CS2H10, and CS2H11 were unveiled under high pressure, which can be viewed as CH4 units inserted into the S-H framework. Given the super-high superconductivity of Im3̄m-SH3, we performed electron-phonon coupling calculations of these compounds,the metastable of R3m-CSH7, Cm-CSH7, Cm-CS2H10, P3m1-CS2H10, Cm-CS2H11, and Fmm2-CS2H11 are predicted to become good phonon-mediated superconductors that could reach Tc of 130, 120, 72, 74, 92, and 70 K at 270 GPa, respectively. Furthermore, we identified that high Tc is associated with the large contribution of the S-H framework to the electron density of states near the Fermi level. Our results highlight the importance of the S-H framework in superconductivity and verify that the suppression of density of states of these carbonaceous sulfur hydrides by CH4 units results in Tc lower than that of Im3̄m-SH3, which could act as a useful guidance in the design and optimization of high-Tc superconductors in these and related systems.