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 (T_c) 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 T_c of 24 K, and the T_c 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 T_c under applied magnetic fields. Our results demonstrate that Mg₂RhH₆ is thermodynamically stable above 30 GPa, establishing it as the first superconductor with a T_c 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.