论文标题
非基塔夫与基塔夫蜂窝
Non-Kitaev vs. Kitaev Honeycomb Cobaltates
论文作者
论文摘要
最近，尽管旋转轨道耦合较弱，但提议与3 $ d^7 $的蜂窝架一起显示kitaev物理。但是，其他理论和实验作品发现了领先的XXZ Heisenberg和Baco $ _2 $（ASO $ _4 $）$ _ 2 $（BCAO）中的XXZ Heisenberg和可忽略不计的Kitaev互动，该公司呼吁进一步研究以阐明差异的起源。在这里，我们使用强耦合扰动理论得出自旋模型的分析表达。通过{\ it ab-initio}获得理想化蜂窝BCAO的计算获得的紧密绑定参数，我们发现最大的Orbital $ T_ {2G} -T_ {2G} -T_ {2G} $交换路径在早期的理论提议中被假定为小的fermagagnetic（fmagnetic（fmagne）（FMAGNETIC（FMAGNETIC（FM））。这成为主要的交互作用，因为其他$ t_ {2g} -e_g $和$ e_g-e_g $贡献几乎相互取消。完全相同的假设通道还会生成反铁磁Kitaev相互作用，然后从$ t_ {2g} -e_g $路径中取消FM Kitaev相互作用，从而导致小型Kitaev相互作用。在三角形失真下，杰出的各向同性海森堡成为了预期的各向异性XXZ模型，而BCAO就是这种情况。但是，在Na $ _3 $ co $ _2 $ _2 $ sbo $ _6 $中，肉内$ t_ {2g} -t_ {2g} $跳跃较小，可与$ t_ {2g} -e_g $跳跃相媲美，从而导致增强的Kitaev和减少Heisenberg互动之间的精致竞争。
Recently, honeycomb cobaltates with 3$d^7$ were proposed to display Kitaev physics despite weak spin-orbit coupling. However, other theoretical and experimental works found leading XXZ Heisenberg and negligible Kitaev interactions in BaCo$_2$(AsO$_4$)$_2$ (BCAO), which calls for a further study to clarify the origin of the discrepancies. Here we derive the analytical expressions of the spin model using strong-coupling perturbation theory. With tight binding parameters obtained by {\it ab-initio} calculations for idealized honeycomb BCAO, we find that the largest intraorbital $t_{2g}-t_{2g}$ exchange path, which was assumed to be small in the earlier theory proposal, leads to a ferromagnetic (FM) Heisenberg interaction. This becomes the dominant interaction, as other $t_{2g}-e_g$ and $e_g-e_g$ contributions almost cancel each other. Exactly the same assumed-to-be-small channel also generates an antiferromagnetic Kitaev interaction, which then cancels a FM Kitaev interaction from $t_{2g}-e_g$ paths, resulting in a small Kitaev interaction. Under the trigonal distortion, the preeminent isotropic Heisenberg becomes an anisotropic XXZ model as expected, which is the case for BCAO. However, in Na$_3$Co$_2$SbO$_6$ the intraorbital $t_{2g}-t_{2g}$ hopping is smaller and comparable to the $t_{2g}-e_g$ hopping, leading to a delicate competition between enhanced Kitaev and reduced Heisenberg interactions.
