Quantum Spin Hall Effect in a Transition Metal Oxide Na₂IrO₃

We study theoretically the electronic states in a 5d transition metal oxide Na₂IrO₃, in which both the spin-orbit interaction and the electron correlation play crucial roles. A tight-binding model analysis together with the first-principles band structure calculation predicts that this material is a layered quantum spin Hall system. Because of the electron correlation, an antiferromagnetic order first develops at the edge, and later inside the bulk at low temperatures. This article reports one of the first studies of topologically non-trivial band structures in a system with correlated electrons. JK from our Institute performed the material specific calculations and contributed essentially to their interpretation.

(a) The honeycomb lattice of Ir atoms in Na₂IrO₃ viewed from the c axis. A large black circle shows an Ir atom surrounded by six O atoms (red small circles). (b) The transfer integrals on the honeycomb lattice. A black solid line shows −t, while blue short-dashed, red dash-dotted, and green long-dashed arrows indicate it′σ_x, it′σ_y, it′σ_z, respectively.

¹Department of Applied Physics, The University of Tokyo, Hongo, Bunkyo-ku, Tokyo 113-8656, Japan
²Cross-Correlated Materials Research Group (CMRG), ASI, RIKEN, Wako 351-0198, Japan
³Theoretical Physics III, Center for Electronic Correlations and Magnetism, Institute of Physics, University of Augsburg, Augsburg 86135, Germany
⁴Institute of Physics, Academy of Sciences of the Czech Republic, Cukrovarnická 10, 162 53 Praha, Czech Republic
⁵Department of Physics, McCullough Building, Stanford University, Stanford, California 94305-4045, USA