Prediction of high-Tc superconductivity in H6SX below megabar pressure

Abstract

The discovery of high critical temperature in cubic H₃S under high pressures attracts significant attention. Of particular recent interest is to search for superconductors stabilized at low pressure in order to approach practical applications. To examine the doping effect on the stability and superconductivity of H₃S, we construct H₆SX by replacing half of the S atoms with an X atom (X = Si, Ge, Sn, P, As, Sb, Te, Cl, Br and I). In addition to previously reported compounds, we identified seven new superconductors that are dynamically stable below 200 GPa, e.g., Fdm H₆SAs, H₆SSb, H₆SI, H₆SSn, H₆STe, Cmmm H₆SCl, H₆SBr. Among these, H₆SSb exhibits T_c of 91 K at 200 GPa, and increases to 115 K as pressure decreases to 40 GPa. Electron–phonon analysis indicates that the coupling between the electron of Sb atoms and the associated low-frequency phonons is responsible for the enhancement of the superconductivity. Additionally, the superconductivity of H₆SSX is closely related to the electronegativity of X in the same main group, where X with a larger electronegativity results in a strong H–X bond, resulting in a higher superconductivity.