Department of Physics and Astronomy, University of British Columbia, Vancouver, British Columbia V6T 1Z1, Canada.
Phys Rev Lett. 2012 Dec 28;109(26):266406. doi: 10.1103/PhysRevLett.109.266406. Epub 2012 Dec 27.
We study Na2IrO3 by angle-resolved photoemission spectroscopy, optics, and band structure calculations in the local-density approximation (LDA). The weak dispersion of the Ir 5d-t(2g) manifold highlights the importance of structural distortions and spin-orbit (SO) coupling in driving the system closer to a Mott transition. We detect an insulating gap Δ(gap)≃340 meV which, at variance with a Slater-type description, is already open at 300 K and does not show significant temperature dependence even across T(N)≃15 K. An LDA analysis with the inclusion of SO and Coulomb repulsion U reveals that, while the prodromes of an underlying insulating state are already found in LDA+SO, the correct gap magnitude can only be reproduced by LDA+SO+U, with U=3 eV. This establishes Na2IrO3 as a novel type of Mott-like correlated insulator in which Coulomb and relativistic effects have to be treated on an equal footing.
我们通过角分辨光电子能谱、光学和局域密度近似（LDA）下的能带结构计算研究了 Na2IrO3。Ir 5d-t(2g)能级的弱色散突出了结构变形和自旋轨道（SO）耦合在驱动系统更接近莫特转变方面的重要性。我们探测到一个绝缘能隙Δ(gap)≃340 meV，与 Slater 型描述不同，该能隙在 300 K 时已经打开，即使在 T(N)≃15 K 附近也没有明显的温度依赖性。包括 SO 和库仑排斥 U 的 LDA 分析表明，尽管在 LDA+SO 中已经发现了潜在绝缘状态的先兆，但只有通过 LDA+SO+U（U=3 eV）才能重现正确的能隙大小，这表明 Na2IrO3 是一种新型的莫特型关联绝缘体，其中库仑和相对论效应必须平等对待。
