一种新的强关联铕超晶格
Novel Strongly Correlated Europium Superhydrides
摘要：
我们在86-130 GPa的压力下对铕的高压化学进行了联合实验-理论研究。我们发现了几种新的非谐效应稳定的磁性Eu超晶格：立方相$EuH_{9}$，六方相$EuH_{9}$，以及一种意想不到的立方（Pm-3 n）笼形相$Eu_{8}H_{46}$。蒙特卡罗模拟表明，立方相$EuH_{9}$具有反铁磁有序性，T（Neel）最高可达24 K，而六方相$EuH_{9}$和Pm-3 n- $Eu_{8}H_{46}$具有铁磁有序性，T（Curie）分别为137和336 K.所有研究的铕的电子-声子相互作用都很弱，它们的磁序排除了s波超导性，除了，也许，对于扭曲的伪六方$EuH_{9}$。DFT+U方法预测的状态方程（线性响应理论中发现了Hubbard修正）与实验数据非常吻合。这项工作表明，原子半径对超晶格结构的破缺畸变及其热力学稳定性有很大影响。
英文摘要：
We conducted a joint experimental-theoretical investigation of the high-pressure chemistry of europium polyhydrides at pressures of 86-130 GPa. We discovered several novel magnetic Eu superhydrides stabilized by anharmonic effects: cubic $EuH_{9}$, hexagonal $EuH_{9}$, and an unexpected cubic (Pm-3n) clathrate phase, $Eu_{8}H_{46}$. Monte Carlo simulations indicate that cubic $EuH_{9}$ has antiferromagnetic ordering with T(Neel) up to 24 K, whereas hexagonal $EuH_{9}$ and Pm-3n-$Eu_{8}H_{46}$ possess ferromagnetic ordering with T(Curie) = 137 and 336 K, respectively. The electron-phonon interaction is weak in all studied europium hydrides, and their magnetic ordering excludes s-wave superconductivity, except, perhaps, for distorted pseudohexagonal $EuH_{9}$. The equations of state predicted within the DFT+U approach (the Hubbard corrections were found within linear response theory) are in close agreement with the experimental data. This work shows the great influence of the atomic radius on symmetry-breaking distortions of the crystal structures of superhydrides and on their thermodynamic stability.
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