First-principles study of the structures and superconductivity of H-S-La systems under high pressure

Recent experimental and theoretical studies have shown that a La-H system displays remarkable superconducting properties, and it is also possible to improve the superconducting state by introducing other elements into this system. In this study, we systematically investigated the crystal structures and physical properties of an H-S-La system by using first-principles calculations combined with the CALYPSO structure exploration technique. We predicted four stable stoichiometries containing H₂SLa, H₃SLa, H₄Sla, and H₆SLa. These compounds undergo a series of phase transitions under 50-300 GPa. The bonding characters and electronic properties were calculated. It was found that Cm-H₂SLa, C2/c-H₂SLa, and Cmcm-H₆SLa exhibit good metallic nature, which stimulates us to further study their superconducting properties. The calculated superconducting transition temperatures (T_c) of Cm-H₂SLa, C2/c-H₂Sla, and Cmcm-H₆SLa are 15.0 K at 200 GPa, 6.9 K at 300 GPa, and 23.6 K at 300 GPa, respectively.