Semi-metallic ground state of hyper-kagome iridate Na3Ir3O8 produced by a competion of molecular orbital split and spin-orbit coupling

T. Takayama, A. Yaresko, A. Matsumoto, J. Nuss, and H. Takagi
A new complex iridium oxide Na3Ir3O8 with the chiral hyper-kagome lattice of Ir ions was synthesized. The average valence of Ir is 4.33+ and, therefore, Na3Ir3O8 can be viewed as a doped analogue of the hyper-kagome spin liquid Na4Ir3O8 with Ir4+. The transport measurements, combined with the electronic structure calculations, indicate that the ground state of Na3Ir3O8 is a low carrier density semi-metal. We argue that the semi-metallic state is produced by a competition of the molecular orbital splitting of t2g orbitals on Ir3 triangles with strong spin-orbit coupling of heavy Ir ions.

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