Observation of metallic surface states in the strongly correlated Kitaev-Heisenberg candidate Na2IrO3

Abstract

We report high-resolution angle-resolved photoemission spectroscopy measurements on the honeycomb iridate Na2IrO3. Our measurements reveal the existence of a metallic surface band feature crossing the Fermi level with nearly linear dispersion and an estimated surface carrier density of 3.2 $\times$ 10${}^{13}$ cm${}^{-2}$, which has not been theoretically predicted or experimentally observed, and provides the first evidence for metallic behavior on the boundary of this material, whereas the bulk bands exhibit a robust insulating gap. We further show the lack of theoretically predicted Dirac cones at the $\overline{M}$ points of the surface Brillouin zone, which confirms the absence of a stacked quantum spin Hall phase in this material. Our data indicates that the surface ground state of this material is exotic and metallic, unlike as predicted in theory, and establishes Na2IrO3 as a rare example of a strongly correlated spin-orbit insulator with surface metallicity.

16 pages, 4 Figures, Supplementary Info

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Cited by in corpus (11)

• Models and Materials for Generalized Kitaev Magnetism
• Interacting topological insulators: a review
• Topological quantum materials from the viewpoint of chemistry
• Three-band Hubbard model for Na${}_2$IrO${}_3$: Topological insulator, zigzag antiferromagnet, and Kitaev-Heisenberg material
• Quasiparticles and charge transfer at the two surfaces of the honeycomb iridate Na${}_2$IrO${}_3$
• Single-hole spectra of Kitaev spin liquids: from dynamical Nagaoka ferromagnetism to spin-hole fractionalization
• Competition between magnetic order and charge localization in Na${}_2$IrO${}_3$ thin crystal devices
• Topological property of a $t_{2g}^5$ system with a honeycomb lattice structure
• Conductivity of Dirac-like surface states in correlated honeycomb transition metal oxide Mott insulators
• Spectrum of the hole excitation in spin-orbit Mott insulator Na${}_2$IrO${}_3$
• Metallic conductivity on Na-deficient structural domain walls in the spin-orbit Mott insulator Na${}_2$IrO${}_3$