AI 中文总结
该研究通过DFT+DMFT计算揭示Eu取代无限层镍氧化物中Eu-4f电子的Hund耦合驱动的局域-巡游二象性，解释了混合价与局域磁矩起源，并预测低能准粒子可能提升超导转变温度。
AI 中文摘要
最近在Eu取代的无限层镍氧化物中发现的再入超导性和升高的$T_c$提出了一个关键问题，即Eu-4$f$态的性质及其与Ni-$d$电子潜在相互作用的问题。这里我们将密度泛函理论与动力学平均场理论（DFT+DMFT）计算相结合，研究镍氧化物112结构中Eu离子的价态和磁性，明确处理Ni-3$d$和Eu-4$f$壳层中的库仑排斥。我们发现Eu-4$f$构型存在由Hund耦合$J_{\ m H}$驱动的三区域演化。实验推断的磁性和混合价Eu离子态仅在中等的$J_{\ m H}$下出现，此时局域磁矩与强关联的$j=7/2$准粒子共存，这与小$J_{\ m H}$下的非磁态和大$J_{\ m H}$下的完全自旋极化二价态形成对比。这种局域-巡游二象性源于由$j=5/2$和$7/2$流形之间的4$f$内电荷转移诱导的有效空穴掺杂的轨道选择性Mott态。这不仅解释了实验观察到的Eu离子混合价和局域磁矩行为的起源，还预测了可能与Ni-3$d$电子杂化并有助于升高$T_c$的低能4$f$准粒子。我们的工作为理解Eu取代的无限层镍氧化物的异常铁磁和超导性质提供了基础。
英文摘要
Recent discovery of reentrant superconductivity and elevated $T_c$ in Eu-substituted infinite-layer nickelates raises a critical question concerning the nature of Eu-4$f$ states and their potential interaction with Ni-$d$ electrons. Here we combine density functional theory with the dynamical mean-field theory (DFT+DMFT) calculations to investigate the valence and magnetic properties of Eu-ions in the nickelate 112 structure, explicitly treating the Coulomb repulsion in both Ni-3$d$ and Eu-4$f$ shells. We find a three-regime evolution of the Eu-4$f$ configuration driven by its Hund's rule coupling $J_{\rm H}$. The magnetic and mixed-valence Eu ionic state inferred by experiments only occurs for moderate $J_{\rm H}$, with coexisting local moments and strongly correlated $j=7/2$ quasiparticles, in contrast to the nonmagnetic state at small $J_{\rm H}$ and the fully spin-polarized divalent state at large $J_{\rm H}$. This local-itinerant duality arises from an effectively hole-doped orbital-selective Mott state induced by the intra-4$f$ charge transfer between $j=5/2$ and $7/2$ manifolds. It not only explains the origin of the mixed-valence and local moment behaviors of the Eu-ions observed experimentally, but also predicts low-energy 4$f$ quasiparticles that may hybridize with the Ni-3$d$ electrons and contribute to the elevated $T_c$. Our work provides a basis for understanding the unusual ferromagnetic and superconducting properties of Eu-substituted infinite-layer nickelates.
