Synthesis and Superconductivity of Ternary A15-(Lu, Y)₄H₂₃ at High Pressures

Ternary hydrides, formed by introducing new elements into binary hydrides, are a crucial pathway for enhancing superconducting transition temperatures (<i>T</i>_c) or reducing the stable pressures. In this work, we have acquired the ternary hydride formed by Lu and Y atoms, inspired by the low stabilization pressure of the Lu-H system with its fully filled 4<i>f</i> electrons, as well as the higher <i>T</i>_c of the Y-H system. By effectively controlling the high-pressure and high-temperature conditions, we have successfully synthesized <i>Pm</i>-3<i>n</i> (Lu, Y)₄H₂₃ (A15-type). The synthesized <i>Pm</i>-3<i>n</i> (Lu, Y)₄H₂₃ reveals the highest <i>T</i>_c of 112 K at 215 GPa, which is the record <i>T</i>_c among A15-type superconductors. Compared to the binary <i>Pm</i>-3<i>n</i> Lu₄H₂₃, the <i>Pm</i>-3<i>n</i> (Lu, Y)₄H₂₃ exhibits a 60% increase in <i>T</i>_c and a 61% enhancement in the upper critical field μ₀<i>H</i>_c2(0). Interestingly, <i>Pm</i>-3<i>n</i> (Lu, Y)₄H₂₃ displays minimal volume expansion and a slight increase in the H-H bond distance relative to <i>Pm</i>-3<i>n</i> Lu₄H₂₃ due to the introduction of Y atoms. Combined theoretical and experimental analyses indicate that the substitution of Lu atoms with Y atoms enhances electron-phonon coupling (EPC) through modified electronic bands and phonon softening caused by the expansion of H-H bonds, collectively driving the significant enhancement of <i>T</i>_c in <i>Pm</i>-3<i>n</i> (Lu, Y)₄H₂₃. Our work demonstrates a crucial strategy for adjusting and enhancing the superconducting performance of hydrides and offers valuable practical experience for developing ternary hydrides.