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Mott transition in multiorbital models for iron pnictides

机译：铁离子多轨道模型中的莫特跃迁

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The bad-metal behavior of the iron pnictides has motivated a theoretical description in terms of a proximity to Mott localization. Since the parent compounds of the iron pnictides contain an even number of 3d electrons per Fe, it is important to determine whether a Mott transition robustly exists and clarify the nature of the possible Mott insulating phases. We address these issues in a minimal two-orbital model and a more realistic four-orbital model for the parent iron pnictides using a slave-spin approach. In the two-orbital model with two electrons per Fe, we identify a single transition from a metal to a Mott insulator, showing that this transition must exist as a result of orbital degeneracy. Depending on the ratio between the inter- and intraorbital Coulomb repulsions, the insulating state can be either a high-spin Mott insulator or a low-spin orbital-Mott insulator. In the four-orbital model with four electrons per Fe, we find a rich phase diagram for the metal-to-insulator transition. At strong Hund's couplings, a localization transition to a high-spin Mott insulator always occurs. At zero and weak Hund's couplings, on the other hand, we find a transition to an intermediate-spin insulating state. This transition can be viewed as an orbitally selective metal-to-insulator transition: the transition to a Mott insulator in the xz and yz orbitals takes place at the same critical coupling as the transition to either a band insulator at zero Hund's coupling or an orbitally polarized insulator at weak but finite Hund's coupling in the xy and x~2 - y~2 orbitals. The implications of our model studies for the physics of iron pnictides and iron chalcogenides are discussed.
机译：铁素化物的不良金属行为激发了关于莫特局部化的理论描述。由于铁肽的母体化合物每Fe包含偶数个3d电子，因此确定是否牢固存在Mott跃迁并弄清可能的Mott绝缘相的性质非常重要。我们使用从旋技术，以最小的两轨模型和更现实的四轨模型解决了这些问题。在每个铁具有两个电子的双轨道模型中，我们确定了从金属到Mott绝缘子的单个跃迁，表明该跃迁必须由于轨道简并而存在。取决于轨道间和轨道内库仑排斥之间的比率，绝缘状态可以是高自旋莫特绝缘子或低自旋莫特绝缘子。在每个铁具有四个电子的四轨道模型中，我们发现了从金属到绝缘体过渡的丰富相图。在牢固的洪德联轴器处，总是会发生向高自旋莫特绝缘子的局部过渡。另一方面，在零和弱的Hund耦合下，我们发现过渡到中间自旋绝缘状态。这种过渡可以看作是轨道上的金属到绝缘体的选择性过渡：xz和yz轨道上向Mott绝缘子的过渡发生在与零洪德耦合或带轨道上的绝缘子过渡相同的临界耦合下。在xy和x〜2-y〜2轨道上处于弱但有限的Hund耦合的极化绝缘子。讨论了我们的模型研究对铁素化物和硫属元素化物物理学的意义。

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