High $T_{\mathrm{c}}$ phase of (H$_{2}$S)$_{2}$H$_{2}$ at high pressures

Hydrogen was predicted to metalize at high pressures and believed to be a room-temperature superconductor. However, metallization of hydrogen is still under debates. As an alternative, hydrogen dominated materials were extensively explored because of their lower metallization pressure. Here I present the high-pressure studies on structures, metallization, and superconductivity of (H$_{2}$S)$_{2}$H$_{2}$ from \textit{ab initio} calculations [1]. At lower pressures, two phases containing H$_{2}$ units are stable with $P$1 (\textless 37 GPa) and \textit{Cccm} (37-111 GPa) symmetries, which are still insulators. Upon further compression, H$_{2}$ units disappear and two intriguing metallic structures with $R$3m and \textit{Im-}3$m$ symmetries are reconstructive above 111 GPa and 180 GPa, respectively. Remarkably, the estimated $T_{\mathrm{c}}$ of \textit{Im-}3$m$ phase at 200 GPa achieves a very high value of 191 $\sim$ 204 K. Moreover, $T_{\mathrm{c}}$ decreases with pressure at an approximate rate (\textit{dT}$_{\mathrm{c}}$/\textit{dP}) of -0.12~K/GPa. Our predicted high $T_{\mathrm{c}}$ and its pressure dependence in \textit{Im-}3$m$ phase are subsequently verified by recent experiments [2]. Our findings support the conjecture that hydrogen-rich materials are a way to achieve a metallic phase with high $T_{\mathrm{c}}$ at accessibly experimental pressures and represent a significant step toward the understanding of high-pressure behavior of metallic hydrogen. \\[4pt] [1] D. Duan, Y. Liu, T. Cui, et al. Sci. Rep., 4, 6968 (2014)\\[0pt] [2] A. P. Drozdov, M. I. Eremets, and I. A. Troyan, arXiv:1412.0460, (2014)