标题： 分子氢化物超导体$BiH_4$对米格尔定理的符合性 显示英文标题

标题： The compliance of the molecular hydride superconductor $BiH_4$ with the Migdal's theorem

摘要： H3S中发现常温超导体后，激发了人们对高压氢化物的实验和理论研究，目的是获得常温超导性。 目前正在进行搜索的有两种主要的氢化物类别：第一类是共价键结合的氢化物（以H3S为代表），第二类是笼型结构的氢化物（以LaH10、YH6、CaH6为代表）。 最近，第三类超导氢化物被发现，其中氢仍保持分子形式，该类别由BaH12和BiH4代表。 在这里，我们分析了BaH12和BiH4的实验数据。 我们发现，在126 GPa < P < 160 GPa的压力范围内，BaH12表现出平均粒径为26纳米且微应变水平较低（0.1\%）的晶粒。 我们还推导出了BaH12和BiH4的德拜温度$\Theta_D$、爱因斯坦温度$\Theta_E$以及电子-声子耦合常数$\Lambda_{e-ph} $。 BiH4中的$\Lambda_{e-ph} $与基于第一性原理计算得到的值显著不同。 对于BiH4推导出的费米温度$T_F = 20,000 K$将其定位在Uemura图中非常规和常规超导体带之间。 这个位置位于共价键结合和笼型氢化物所在带之外。 BiH4的比率$\Theta_D / T_F = 0.026 $与纯金属和A-15合金典型。 这意味着BiH4是符合Migdal定理的第一个氢化物超导体。 显示英文摘要

摘要： The discovery of near-room-temperature superconductivity in H3S sparked experimental and theoretical studies of highly compressed hydrides with the aim of obtaining room-temperature superconductivity. There are two dominant hydride classes where the search is ongoing: the first class is the covalently bonded hydrides (which is represented by H3S), and the second class is the clathrate-type hydrides (which is represented by LaH10, YH6, CaH6). Recently, the third class of superconducting hydrides, where the hydrogen remains its molecular form, has been discovered. This class is represented by BaH12 and BiH4. Here, we analyzed experimental data for the BaH12 and BiH4. We found that the BaH12 exhibits grains of an average size of 26 nm and a low level of microstrain 0.1%, in the range of 126 GPa < P < 160 GPa. We also derived the Debye $\Theta_D$ and Einstein $\Theta_E$ temperatures, and the electron-phonon coupling constant $\Lambda_{e-ph} $ in BaH12 and BiH4. The $\Lambda_{e-ph} $ in BiH4 significantly differs from the values obtained by first-principles calculations. The derived Fermi temperature $T_F = 20,000 K$ for BiH4 positions this molecular hydride between the unconventional and conventional superconductors bands in the Uemura plot. This position is outside of the band where covalently bonded and clathrate hydrides are located. The ratio $\Theta_D / T_F = 0.026 $ of BiH4 is typical for pure metals and A-15 alloys. This implies that the BiH4, is the first hydride superconductor which complains with the Migdal's theorem.