Interplay of spin-orbit effects and electron delocalization in honeycomb iridates

Condensed Matter Seminars

Speaker: Kateryna Foyevstova, University of British Columbia
Date & Time: January 30, 2014 14:00 - 15:00
Location: UBC, Hennings 318
Local Contact: George Sawatzky
Intended Audience: Graduate

Strong relativistic spin-orbit coupling in iridium oxides gives rise to new interesting physical effects, such as spin-orbit coupling induced Mott insulating state and anisotropic spin exchange. In honeycomb iridates, e.g., Na2IrO3, the peculiar topology of the Ir lattice introduces additional complexity. Recently, it has been proposed that Na2IrO3 might be a realization of the exotic Heisenberg-Kitaev spin model featuring a rich variety of quantum phases [Jackeli and Khaliullin, Phys. Rev. Lett. 102, 017205 (2009)]. However, our detailed DFT studies of the electronic  structure of Na2IrO3 have revealed an important bandstructure effect: the t2g Ir electrons delocalize over Ir hexagons forming quasi-molecular orbitals [Mazin, Jeschke, Foyevtsova, Valenti, and Khomskii, Phys. Rev. Lett. 109, 197201 (2012)]. We argue that due to the significant electron delocalization, a model based on quasi-molecular orbitals might be a better starting point in describing the physics of honeycomb iridates.