AI 中文总结
研究超导氢化镧（LaH$_{10}$）的结构相变，发现其$R\bar{3}m$到$Fm\bar{3}m$转变由四极$T_{2g}$序参量触发，结合MACE神经网络势等方法揭示该弱一级相变与光学$T_{2g}$声子软化相关，为高$T_c$超导体发现提供指导。
AI 中文摘要
氢化镧（LaH$_{10}$）因在约170 GPa压力下具有250 K的超导临界温度而被广泛研究。尽管该材料中与超导相出现相关的结构$R\bar{3}m$到$Fm\bar{3}m$的压力转变已被广泛理解，但其转变的本质和序参量的详细表征仍缺失。通过对氢亚晶格应用簇多极矩分析，我们揭示该转变由四极$T_{2g}$序参量触发，并提供其弱一级性质的证据。通过执行路径积分分子动力学并结合基于Perdew-Burke-Ernzerhof（PBE）密度泛函理论构型训练的消息传递原子簇展开（MACE）神经网络势，我们表明转变时序参量的崩溃同时与光学$T_{2g}$声子的不连续软化相关。它们的对称性使其在LaH$_{10}$中承载不可忽略的电声耦合，而转变的弱一级性质使其软化。具有低频四极畸变的结构不稳定性的存在，可能是增强超氢化物中超导性的关键因素，并为在富氢化合物中发现新的高临界温度（$T_c$）超导体提供指导。
英文摘要
Lanthanum hydride (LaH$_{10}$) has been widely studied for its high superconducting critical temperature of 250 K at about 170 GPa pressure. Although the structural ${R\bar{3}m}$-to-${Fm\bar{3}m}$ transition under pressure connected to the emergence of the superconducting phase in this material is broadly understood, the detailed characterization of its nature and its order parameter are still missing. By applying the cluster multipole moment analysis to the hydrogen sublattice, we reveal that this transition is triggered by a quadrupolar $T_{2g}$ order parameter, and we provide evidence for its weak first-order nature. By performing path integral molecular dynamics coupled to a message-passing atomic cluster expansion (MACE) neural network potential, trained on Perdew-Burke-Ernzerhof (PBE) density functional theory configurations, we show that the collapse of the order parameter at the transition is simultaneously associated with the discontinuous softening of the optical $T_{2g}$ phonons. Their symmetry lets them carry a non-negligible electron-phonon coupling in LaH$_{10}$, while the weak first-order nature of the transition makes them soft. The presence of structural instabilities with low-frequency quadrupolar distortions can be a key ingredient to enhance superconductivity in superhydrides and provides guidance for the discovery of new high-$T_c$ superconductors in hydrogen-rich compounds.
Comments24 pages, 6 figures in the main text, 7 figures in extended data
