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arXiv 2011.10842cond-mat.str-el
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层状钙钛矿材料CsVF $_4$中的轨道有序

Orbital ordering in the layered perovskite material CsVF$_4$

Ling-Fang Lin, Nitin Kaushal, Yang Zhang, Adriana Moreo, Elbio Dagotto

备注：
10 pages, 12 figures
发表信息：
Phys. Rev. Materials 5, 025001 (2021)
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摘要：

在强关联电子系统中，轨道自由度会引起一些新的物理性质。特别地，费米能级附近的轨道简并导致自发对称性破缺，例如FeSe中的基态和几种钙钛矿系统中的轨道有序。在这里，新的层状钙钛矿材料CsVF $_4$，与$3d^2$电子配置，系统地研究了使用密度泛函理论和Hatree-Fock近似内的多轨道Hubbard模型。结果表明，CsVF $_4$应该是磁性的，在$ab$平面上具有G型反铁磁排列，沿$c$ -轴方向具有弱的反铁磁交换，这与实验结果一致.由于VF $_6$八面体中的Jahn-Teller畸变缩短了$c$ -轴，该系统显示出有趣的电子占据$d_{xy}^1(d_{xz}d_{yz})^1$，对应于较低的非简并$d_{xy}$轨道被半填充，而另外两个简并$d_{yz}$和$d_{xz}$轨道每个位点共享一个电子。我们发现，这种简并被打破，一个新的$d_{yz}$ / $d_{xz}$交错轨道模式在这里预测的第一性原理和Hubbard模型计算。这种轨道排序是由与简并去除相关的电子不稳定性驱动的，以降低能量。

英文摘要：

In strongly correlated electronic systems, several novel physical properties are induced by the orbital degree of freedom. In particular, orbital degeneracy near the Fermi level leads to spontaneous symmetry breaking, such as the nematic state in FeSe and the orbital ordering in several perovskite systems. Here, the novel layered perovskite material CsVF$_4$, with a $3d^2$ electronic configuration, was systematically studied using density functional theory and a multiorbital Hubbard model within the Hatree-Fock approximation. Our results show that CsVF$_4$ should be magnetic, with a G-type antiferromagnetic arrangement in the $ab$ plane and weak antiferromagnetic exchange along the $c$-axis, in agreement with experimental results. Driven by the Jahn-Teller distortion in the VF$_6$ octahedra that shorten the $c$-axis, the system displays an interesting electron occupancy $d_{xy}^1(d_{xz}d_{yz})^1$ corresponding to the lower nondegenerate $d_{xy}$ orbital being half-filled and the other two degenerate $d_{yz}$ and $d_{xz}$ orbitals sharing one electron per site. We show that this degeneracy is broken and a novel $d_{yz}$/$d_{xz}$ staggered orbital pattern is here predicted by both the first-principles and Hubbard model calculations. This orbital ordering is driven by the electronic instability associated with degeneracy removal to lower the energy.

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