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首页> 外文期刊>Physical review >Lattice distortion effects on topological phases in (LaNiO_3)_2/(LaAlO_3)_N heterostructures grown along the [111] direction
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Lattice distortion effects on topological phases in (LaNiO_3)_2/(LaAlO_3)_N heterostructures grown along the [111] direction

机译：晶格畸变对沿[111]方向生长的（LaNiO_3）_2 /（LaAlO_3）_N异质结构拓扑相的影响

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摘要

We theoretically investigate the influence of lattice distortion effects on possible topological phases in (LaNiO_3)_2/(LaAlO_3)_N heterostructures grown along the [111] direction. At the Hartree-Fock level, topological phases originate from an interaction-generated effective spin-orbit coupling that opens a gap in the band structure. For the unstrained system, there is a quadratic band touching at the Γ point at the Fermi energy for spin-unpolarized electrons and Dirac points at K, K' at the Fermi energy for fully spin-polarized electrons. Using density functional theory we first show that the quadratic band touching and Dirac points are remarkably stable to internal strain-induced out-of-plane distortions and rotations of the oxygen octahedra, which we compute. The lack of a gap opening implies that the mean-field predictions for topological phases for both the polarized and unpolarized systems are little affected by internal strain and lattice relaxations. On the other hand, we also discuss two types of lattice distortions, which have an important effect on the electronic structure. First, an external strain imposed along the [001] cubic direction can open a gap at the Γ point, thereby stabilizing a trivial insulating phase in the spin-unpolarized system. However, it leaves the Dirac points intact. As a result, the Hartree-Fock calculation for an effective model using parameters relevant to LaNiO_3 finds that symmetry-breaking strain favors a phase with polarized orbitals and antiferromagnetic spin order, but leaves earlier predictions for a zero-magnetic field topological quantum Hall state essentially unchanged. Second, we identify a possible breathing distortion of the oxygen cages stabilized by correlation effects. Such a distortion opens a gap at the Dirac points and we demonstrate that it would compete with the topological phase in the fully spin-polarized system. Taken together, our results suggest that distortion effects in thin films grown along the [111] direction in perovskites have rather different consequences as compared to those grown along [001].
机译：我们从理论上研究了沿[111]方向生长的（LaNiO_3）_2 /（LaAlO_3）_N异质结构中晶格畸变效应对可能的拓扑相的影响。在Hartree-Fock层次上，拓扑阶段源自相互作用生成的有效自旋轨道耦合，从而在能带结构中产生了缺口。对于非应变系统，对于自旋非极化电子，在费米能量的Γ点处有一个接触的二次带，对于完全自旋极化的电子，在费米能量处的K，K'处有一个狄拉克点。使用密度泛函理论，我们首先表明，二次带接触点和狄拉克点对内部应变引起的氧八面体的面外畸变和旋转非常稳定，这是我们计算得出的。缺乏缺口意味着在极化和非极化系统中，拓扑相的平均场预测几乎不受内部应变和晶格弛豫的影响。另一方面，我们还讨论了两种类型的晶格畸变，它们对电子结构具有重要影响。首先，沿[001]立方方向施加的外部应变可以在Γ点打开一个缝隙，从而稳定了自旋非极化系统中的琐碎绝缘相。但是，它使狄拉克点保持不变。结果，使用与LaNiO_3相关的参数对有效模型进行Hartree-Fock计算，发现对称断裂应变有利于具有极化轨道和反铁磁自旋阶数的相，但基本上没有对零磁场拓扑量子霍尔态进行早期预测。不变。其次，我们确定了可能因相关效应而稳定的氧气笼呼吸变形。这种扭曲在Dirac点上打开了一个缺口，我们证明了它会与完全自旋极化系统中的拓扑相竞争。综上所述，我们的结果表明，与沿[001]方向生长的薄膜相比，沿钙钛矿方向[111]方向生长的薄膜的畸变效应具有相当不同的结果。

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