Computational discovery of a dynamically stable cubic ${\mathrm{SH}}_3$-like high-temperature superconductor at 100 GPa via ${\mathrm{CH}}_4$ intercalation

The 203 K superconductivity of ${\mathrm{SH}}_3$ stimulates enormous interest in searching for high-temperature superconductors in compressed hydrides. While several hydrides show high-temperature superconductivity ($>180\mathrm{K}$) at extremely high pressure, it is highly desired to design hydrides that can achieve similar superconductivity at relatively lower pressure. In this work we identify a cubic structure in ternary ${\mathrm{CSH}}_7$ that can be viewed as methane (${\mathrm{CH}}_4$) molecules inserted into the ${\mathrm{SH}}_3$ host lattice as a guest. Ionic bonding in this special host-guest arrangement acts as a chemical precompression for ${\mathrm{SH}}_3$, leading to a much lower predicted dynamically stable pressure of 100 GPa for ${\mathrm{CSH}}_7$ than that of ${\mathrm{SH}}_3$ at 170 GPa. Given the superhigh superconductivity of the parent ${\mathrm{SH}}_3$ sublattice, we performed electron-phonon coupling calculations to estimate the $T_c$ of ${\mathrm{CSH}}_7$ at high pressure, which could reach 181 K at 100 GPa. Our results may shed light on the design principle for other multinary host-guest high-temperature superconducting hydrides with low stable pressure.

Figure 1

(a) Calculated stability of the C-S-H system at 100 GPa. Colored squares denote metastable phases with different formation enthalpies. Purple circles indicate stable phases. (b) Bonding behavior and band gap of C-S-H ternary compounds with formation enthalpies below 50 meV/atom at 100 GPa. Colored triangles, squares, pentagons, and hexagons represent different configurations of the S-H sublattice, respectively. Compounds in red or blue are metallic or nonmetallic.

Figure 2

Conventional cells of (a) $I\overline{4}3m\text{−}{\mathrm{CSH}}_7$, (b) $Im\overline{3}m\text{−}{\mathrm{SH}}_3$, and (c) $Pm\overline{3}m\text{−}{\mathrm{XeSH}}_3$. The large, medium, and small spheres represent the Xe, S, and H atoms, respectively, and the translucent regular tetrahedrons represent the ${\mathrm{CH}}_4$ molecules. Purple lattices represent the $\left[{\mathrm{SH}}_3\right]$ host lattice in a unit. (d) ELF in (1 1 0) direction for $I\overline{4}3m\text{−}{\mathrm{CSH}}_7$ (left panel) at 100 GPa, $Im\overline{3}m\text{−}{\mathrm{SH}}_3$ (middle panel) at 200 GPa, and $Pm\overline{3}m\text{−}{\mathrm{XeSH}}_3$ (right panel) at 100 GPa. Black dotted lines represent the ionic bonds between the host $\left[{\mathrm{SH}}_3\right]$ lattice and the guest ${\mathrm{CH}}_4$ molecules in $I\overline{4}3m\text{−}{\mathrm{CSH}}_7$.

Figure 3

Electronic band structure (left panel) and projected density of states (right panel) of (a) $I\overline{4}3m\text{−}{\mathrm{CSH}}_7$ at 120 GPa and (b) $Im\overline{3}m\text{−}{\mathrm{SH}}_3$ at 200 GPa.

Figure 4

Pressure dependence of $T_c$ in sulfur hydride. Filled circles show experimental results reported by Drozdov et al. [15] while half-filled squares, circles, and stars indicate theoretical results of $I\overline{4}3m\text{−}{\mathrm{CSH}}_7$ in this work, $Im\overline{3}m\text{−}{\mathrm{SH}}_3$ reported by Huang et al. [72], and $Pm\overline{3}m\text{−}{\mathrm{XeSH}}_3$ reported by Li et al. [36], respectively.