Superconducting Hydride Mg2RhH6 Experimentally Achieved at Lower Pressure

Although tremendous progress has been made in recent years in the field of polyhydride superconductors, the realization of high critical temperature (Tc) superconductivity still relies on formidable high pressures. Searching for superconducting hydrides at lower pressures is of particular importance. Here we report the first experimental synthesis of Mg2RhH6, which exhibits superconductivity under a significantly reduced pressure of 30 GPa. The synthesis of Mg2RhH6 proceeds via a two-step process: (1) preparing the Mg2RhH5 precursor, in which hydrogen atoms are stabilized by covalent bonds, and (2) introducing additional hydrogen, which injects electrons into antibonding orbitals above 30 GPa and simultaneously triggers a structural transition from RhH5 square pyramids to RhH6 octahedra. Superconductivity emerges at ∼30 GPa with a Tc of 24 K, and the Tc is further enhanced to 29 K upon synthesis at 53 GPa, as evidenced by a sharp drop to zero resistivity and the characteristic suppression of Tc under applied magnetic fields. Our results demonstrate that Mg2RhH6 is thermodynamically stable above 30 GPa, establishing it as the first superconductor with a Tc of approximately 30 K at a readily accessible pressure. This study pioneers a highly promising pathway for the rational design and discovery of high-temperature superconductors within the phonon-mediated BCS framework.