Spin-orbit coupling induced semi-metallic state in the 1/3 hole-doped hyper-kagome Na3Ir3O8

Abstract

The complex iridium oxide Na3Ir3O8 with a B-site ordered spinel structure was synthesized in single crystalline form, where the chiral hyper-kagome lattice of Ir ions, as observed in the spin-liquid candidate Na4Ir3O8, was identified. The average valence of Ir is 4.33+ and, therefore, Na3Ir3O8 can be viewed as a doped analogue of the hyper-kagome spin liquid 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 inherent to heavy Ir ions.

Short-Range Correlations in the Magnetic Ground State ofNa4Ir3O8

“…1. We found that Na-438 gradually decomposes upon exposure to atmosphere into Na 3+x Ir 3 O 8 with a structure similar to the recently reported Na-338 structure [12]; hence care was taken to minimize its exposure to air and samples were manipulated in an inert atmosphere. This behavior is similar to the decomposition reported in another high alkali content iridate, Na 2 IrO 3 [17].…”

“…2 (b), and the structural conversion can be tracked via x-ray measurements [16]. We note here that hightemperature M (T ) data of Na-338 exhibits a positive slope [12], and hence any admixture of Na-338 within Na-438 will increase the apparent value for Θ CW (Fig. 2 (b) inset).…”

Frozen State and Spin Liquid Physics inNa4Ir3O8: An

“…This has led theorists to promote, for example, the Heisenberg-Kitaev model [19] and the spin-orbit Mott insulator [20]. Na 4 Ir 3 O 8 also appears to be close to an insulator-metal transition [21][22][23][24][25] and weak Mottness has been proposed as a possible scenario for a spin-liquid ground state [26,27], like in the case of organic triangular spin-liquids [12].The macroscopic susceptibility, χ, is typical of J eff = 1 2 moments with antiferromagnetic interactions J ∼ 300 K [14,28]. Heat capacity, C, shows no sign of a bulk transition and has two remarkable features: at 24 K ∼ J/10 a broad maximum and at low temperatures C = γT + βT n where 2 < n < 3 [14,21].…”

“…This has led theorists to promote, for example, the Heisenberg-Kitaev model [19] and the spin-orbit Mott insulator [20]. Na 4 Ir 3 O 8 also appears to be close to an insulator-metal transition [21][22][23][24][25] and weak Mottness has been proposed as a possible scenario for a spin-liquid ground state [26,27], like in the case of organic triangular spin-liquids [12].…”

“…(ii) The transition to metallicity, observed either under pressure [45] or in depleted Na samples [21][22][23][24], might indicate the proximity to a quantum critical point. In this context, modeling has focused on the metallic rather than insulating side [26,27]; here, the T −dependence of T −1 1 is a crucial test.…”