Novel phases and superconductivity in indium sulfides under pressure

Recent studies of sulfides have highlighted their potential for exploring unique superconductors under pressure. Here we combine crystal structure predictions with ab initio calculations on the crystal structures, electronic structures and superconducting properties of the In-S system within 80 GPa. We predicted six unique In-S sulfides within five stoichiometries. Among them, In2S-C2/m, InS-Fm-3m and InS-Pmmn are thermodynamically stable within certain pressure ranges, whereas In3S-P4/nmm, InS5-P21/m and InS6-P-6 are meta-stable. With the increase of S content, we can observe varied contributions to electronic structures from In and S atoms, and the S-rich phases correspond to better superconductivity in our predicted In-S sulfides. In particular, the S-rich sulfides of InS5-P21/m and InS6-P-6 stand out with the estimated Tc of about 11 K at 40 GPa and 13 K at 20 GPa, respectively. By analyzing the correlation between bond strength and Tc values of other six binary sulfide systems, we summarized preliminary strategies for designing superconducting sulfides. Our work is helpful for further understanding the phase diagram of In-S system under high pressure, and could provide theoretical support for studying unique superconducting sulfides in experiments.