Strongly frustrated triangular spin lattice emerging from triplet dimer formation in honeycomb Li2IrO3
Abstract
In quantum magnetism spin dimers are typically associated with spin-singlet states. To date, triplet dimerization has not been observed in any 3D or quasi-2D material. With this in mind we here discuss the electronic structure of the spin-orbit driven 5d5 Mott insulator Li2IrO3, a honeycomb-lattice system with two crystallographically inequivalent Ir-Ir bonds. From ab initio many-body calculations we find that, while both Heisenberg and Kitaev couplings are present, the magnetic interactions are dominated by a strong isotropic ferromagnetic exchange on only one set of bonds. This causes the formation of triplet spin dimers effectively placed on a strongly frustrated triangular lattice. The triplet dimers remain protected in a large region of the phase diagram, suggesting that Li2IrO3 has a long-range incommensurate magnetic ground state that is pushed by the Kitaev exchange interactions beyond a standard planar helix configuration.
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