A-15型超导氢化物$La_4H_{23}$：具有低应变、强电声相互作用和中等非绝热水平的纳米晶结构
A-15 type superconducting hydride $La_4H_{23}$: Nanograined structure with low strain, strong electron-phonon interaction, and moderate level of nonadiabaticity
AI总结：
本研究分析A-15型超导氢化物$La_4H_{23}$的实验数据，揭示其纳米晶低应变结构、强电声耦合与中等非绝热性，证实其属于非常规超导体，刷新A-15家族超导温度纪录。
AI中文摘要：
七十年来，我们所说的A-15超导体指的是由Hardy和Hulm（《物理评论》89卷，884页，1953年）发现的金属性$A_3B$合金（其中A为过渡金属，B为IIIB族和IVB族元素）。在这些合金中，$Nb_3Ge$表现出最高的超导转变温度$T_c = 23\rm\thinspace K$，而$Nb_3Sn$是现代应用超导领域的核心材料。\n近期，Guo等人（arXiv:2307.13067）通过观测发现在$P = 118\rm\thinspace GPa$压强下压缩的$La_4H_{23}$相零电阻超导转变温度$T_{c,zero} = 81\rm\thinspace K$，拓展了金属离子排列为β钨（A-15）亚晶格的超导体家族。尽管与Drozdov等人（《自然》569卷，531页，2019年）发现的近室温超导$LaH_{10}$相（$P = 200\rm\thinspace GPa$下$T_{c,zero} = 250\rm\thinspace K$）相比，$La_4H_{23}$的$T_c$低得多，但它保持着A-15家族中最高的$T_c$纪录。Cross等人（《物理评论B》109卷，L020503页，2024年）证实了受压$La_4H_{23}$的高温超导性。\n本文中，我们分析了已测得的$La_4H_{23}$实验数据，发现该超导体具有纳米晶结构（晶粒尺寸$5.5\rm\thinspace nm < D < 35\rm\thinspace nm$）、低晶体应变（<0.003）、高电声耦合常数（$1.5 < λ_{e-ph} < 2.55$）以及中等水平的非绝热性$Θ_{D}/T_{F}$。我们发现，$La_4H_{23}$相推导得到的$Θ_{D}/T_{F}$和$T_c/T_F$值与铜氧化物、铁基超导体以及近室温超导体$H_3S$和$LaH_{10}$中的对应值相似，这表明$La_4H_{23}$相落在植村（Uemura）图中的非常规超导体区域内。
英文摘要：
For seven decades by A-15 superconductors we meant metallic $A_3B$ alloys (where A is a transition metal, and B is groups IIIB and IVB element) discovered by Hardy and Hulm (Phys. Rev. 89, 884 (1953)). Nb3Ge exhibited the highest superconducting transition temperature, $T_c = 23 K$, among these alloys. One of these alloys, $Nb_3Sn$, is primary material in modern applied superconductivity. Recently Guo et al (arXiv:2307.13067) extended the family of superconductors where the metallic ions arranged in the beta tungsten (A-15) sublattice by observation of $T_{c,zero} = 81 K$ in $La_4H_{23}$ phase compressed at $P = 118 GPa$. Despite the $La_4H_{23}$ has much lower $T_c$ in comparison with near-room-temperature superconducting $LaH_{10}$ phase ($T_{c,zero} = 250 K$ at $P = 200 GPa$) discovered by Drozdov et al (Nature 569, 531 (2019)), the $La_4H_{23}$ holds the record high $T_c$ within A-15 family. Cross et al (Phys. Rev. B 109, L020503 (2024)) confirmed the high-temperature superconductivity in the compressed $La_4H_{23}$. In this paper, we analyzed available experimental data measured in $La_4H_{23}$ and found that this superconductor exhibits nanograined structure, 5.5 nm < D < 35 nm, low crystalline strain < 0.003, high electron-phonon coupling constant, 1.5 < $λ_{e-ph}$ < 2.55, and moderate level of the nonadiabaticity $Θ_{D}/T_{F}$. We found that derived $Θ_{D}/T_{F}$ and $T_c/T_F$ values for the $La_4H_{23}$ phase are similar to the ones in cuprates, pnictides, and near-room-temperature superconductors $H_3S$ and $LaH_{10}$, which implies that the $La_4H_{23}$ phase falls to unconventional superconductors band in the Uemura plot.
