Kitaev interactions between j=1/2 moments in honeycomb Na2IrO3 are large and ferromagnetic: insights from ab initio quantum chemistry calculations
Kitaev interactions between j=1/2 moments in honeycomb Na2IrO3 are large and ferromagnetic: insights from ab initio quantum chemistry calculations
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DOI：
10.1088/1367-2630/16/1/013056
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发表时间：
2014-01-31
影响因子：
3.3
通讯作者：
van den Brink, Jeroen
中科院分区：
文献类型：
--
作者：
Katukuri, Vamshi M.;Nishimoto, S.;van den Brink, Jeroen
Na2IrO3是一种蜂窝5d(5)氧化物，最近被认为是基塔耶夫自旋晶格的潜在实现。这个自旋模型的基本特征是，对于从一个金属位点产生的三个金属-金属链接中的每一个，基塔耶夫相互作用只连接垂直于由磁性离子和两个桥接配体定义的斑块的自旋组件。相互正交的自旋分量沿三个不同环节耦合的事实导致了强挫折效应和非平凡物理。虽然实验表明Na2IrO3的反铁磁顺序为之字形，但Kitaev和Heisenberg相互作用的符号和相对强度仍在争论中。本文报告了从头计算多体电子结构的结果，并确定了最近邻居交换是强各向异性的，主要是铁磁基塔伊夫部分，而海森堡贡献明显较弱，并且是反铁磁的。计算进一步揭示了对微小结构细节（如键角）的强烈敏感性。除了大的自旋轨道相互作用外，这种对Ir2O2斑块畸变的强烈依赖使蜂窝5d(5)氧化物成为在扩展系统中实现非常规磁基态和激发的新场所。
Na2IrO3, a honeycomb 5d(5) oxide, has been recently identified as a potential realization of the Kitaev spin lattice. The basic feature of this spin model is that for each of the three metal-metal links emerging out of a metal site, the Kitaev interaction connects only spin components perpendicular to the plaquette defined by the magnetic ions and two bridging ligands. The fact that reciprocally orthogonal spin components are coupled along the three different links leads to strong frustration effects and nontrivial physics. While the experiments indicate zigzag antiferromagnetic order in Na2IrO3, the signs and relative strengths of the Kitaev and Heisenberg interactions are still under debate. Herein we report results of ab initio many-body electronic-structure calculations and establish that the nearest-neighbor exchange is strongly anisotropic with a dominant ferromagnetic Kitaev part, whereas the Heisenberg contribution is significantly weaker and antiferromagnetic. The calculations further reveal a strong sensitivity to tiny structural details such as the bond angles. In addition to the large spin-orbit interactions, this strong dependence on distortions of the Ir2O2 plaquettes singles out the honeycomb 5d(5) oxides as a new playground for the realization of unconventional magnetic ground states and excitations in extended systems.