After the significant discovery of the hole-doped nickelate compound Nd_0.8Sr_0.2NiO₂, an analysis of the electronic structure, orbital components, Fermi surfaces and band topology could be helpful to understand the mechanism of its superconductivity. Based on the first-principles calculations, we find that Ni |$3d_{x^2-y^2}$| states contribute the largest Fermi surface. |$Ln~5d_{3z^2-r^2}$| states form an electron pocket at Γ, while 5d_xy states form a relatively bigger electron pocket at A. These Fermi surfaces and symmetry characteristics can be reproduced by our two-band model, which consists of two elementary band representations: B_1g@1a ⊕ A_1g@1b. We find that there is a band inversion near A, giving rise to a pair of Dirac points along M–A below the Fermi level upon including spin-orbit coupling. Furthermore, we have performed the DFT+Gutzwiller calculations to treat the strong correlation effect of Ni 3d orbitals. In particular, the bandwidth of |$3d_{x^2-y^2}$| has been renormalized largely. After the renormalization of the correlated bands, the Ni 3d_xy states and the Dirac points become very close to the Fermi level. Thus, a hole pocket at A could be introduced by hole doping, which may be related to the observed sign change of Hall coefficient. By introducing an additional Ni 3d_xy orbital, the hole-pocket band and the band inversion can be captured in our modified model. Besides, the nontrivial band topology in the ferromagnetic two-layer compound La₃Ni₂O₆ is discussed and the band inversion is associated with Ni |$3d_{x^2-y^2}$| and La 5d_xy orbitals.

中文翻译：

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镍酸盐中的电子结构和拓扑性质 Lnn + 1NinO2n + 2

空穴掺杂镍酸盐化合物Nd _0.8 Sr _0.2 NiO ₂的重大发现后，对其电子结构、轨道分量、费米面和能带拓扑结构的分析有助于理解其超导性的机理。根据第一性原理计算，我们发现 Ni |$3d_{x^2-y^2}$| 态贡献最大的费米面。|$Ln~5d_{3z^2-r^2}$| 态在 Γ 处形成一个电子袋，而 5 d _xy态在 A 处形成一个相对较大的电子袋。这些费米面和对称特性可以通过我们的双能带模型重现，该模型由两个基本能带表示：B _1g @1 a  ⊕  A _{1 g} @1 b。我们发现在 A 附近有一个带反转，在包括自旋轨道耦合后，在费米能级下方沿 M-A 产生一对狄拉克点。此外，我们已经执行了 DFT+Gutzwiller 计算来处理 Ni 3d 轨道的强相关效应。特别是|$3d_{x^2-y^2}$|的带宽 已在很大程度上重新规范化。在相关带重整化后，Ni 3 d _xy态和狄拉克点变得非常接近费米能级。因此，空穴掺杂可以在 A 处引入空穴袋，这可能与观察到的霍尔系数符号变化有关。通过引入额外的 Ni 3d _xy轨道，孔袋带和带反转可以在我们的修改模型中捕获。此外，讨论了铁磁两层化合物La ₃ Ni ₂ O _{6 中}的非平凡能带拓扑结构，能带反转与Ni |$3d_{x^2-y^2}$|有关。和 La 5 d _xy轨道。