Superconductivity in ternary hydrides at high pressure

As one of the 25 physics challenges in this century, high-temperature superconductivity has been of concern for a long time. According to BCS theory, superconductivity is possible if three conditions are met, which are high-frequency phonons, strong electron-phonon coupling, and a high density of states. In theory, the metallic state of hydrogen and hydride under high pressure can satisfy the above conditions. Several binary hydride systems have been experimentally proved to be high-temperature superconductors (HTSs) at high pressure. Ternary hydrides can be regarded as the doping of binary hydrides, which have broad prospects. At present, in both experimental and theoretical research, ternary hydrides are the record holder for the highest superconducting critical temperature (T-c) which is 287 K in C-H-S system, and 473 K in Li-Mg-H system, respectively. This review will systematically describe the research status of superconductivity on ternary hydride at high pressure. Relevant theoretical research was classified according to different binary hydride doping systems. The experimental research was then introduced. In terms of experimental research, we focus on the latest research of C-S-H and La-Y-H HTSs, and overview the subsequent studies about high T-c of C-S-H system.