Synthesis and Superconductivity of Ternary A15-(Lu, Y)<sub>4</sub>H<sub>23</sub> at High Pressures
Kexin Zhang, Jingkun Yu, Yuchen Zhang, Jianning Guo, Yulong Wang, Chuang Jiang, Xiaoli Huang, Tian Cui
Abstract
Ternary hydrides, formed by introducing new elements into binary hydrides, are a crucial pathway for enhancing superconducting transition temperatures ( T 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 f electrons, as well as the higher T c of the Y–H system. By effectively controlling the high-pressure and high-temperature conditions, we have successfully synthesized Pm -3 n (Lu, Y) 4 H 23 (A15-type). The synthesized Pm -3 n (Lu, Y) 4 H 23 reveals the highest T c of 112 K at 215 GPa, which is the record T c among A15-type superconductors. Compared to the binary Pm -3 n Lu 4 H 23, the Pm -3 n (Lu, Y) 4 H 23 exhibits a 60% increase in T c and a 61% enhancement in the upper critical field μ 0 H c2 (0). Interestingly, Pm -3 n (Lu, Y) 4 H 23 displays minimal volume expansion and a slight increase in the H–H bond distance relative to Pm -3 n Lu 4 H 23 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 T c in Pm -3 n (Lu, Y) 4 H 23 . Our work demonstrates a crucial strategy for adjusting and enhancing the superconducting performance of hydrides and offers valuable practical experience for developing ternary hydrides.