Phase Diagram and Quantum Order by Disorder in the Kitaev K1 − K2 Honeycomb Magnet
journal contributionposted on 06.08.2018 by Ioannis Rousochatzakis, Johannes Reuther, Ronny Thomale, Stephan Rachel, Natalia B. Perkins
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We show that the topological Kitaev spin liquid on the honeycomb lattice is extremely fragile against the second-neighbor Kitaev coupling K2, which has recently been shown to be the dominant perturbation away from the nearest-neighbor model in iridate Na2IrO3, and may also play a role in α-RuCl3and Li2IrO3. This coupling naturally explains the zigzag ordering (without introducing unrealistically large longer-range Heisenberg exchange terms) and the special entanglement between real and spin space observed recently in Na2IrO3. Moreover, the minimal K1- K2model that we present here holds the unique property that the classical and quantum phase diagrams and their respective order-by-disorder mechanisms are qualitatively different due to the fundamentally different symmetries of the classical and quantum counterparts.
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I. R. and N. B. P. acknowledge support from NSF Grant No. DMR-1511768. J. R. was supported by the Freie Universitat Berlin within the Excellence Initiative of the German Research Foundation. R. T. was supported by the European Research Council through ERC-StG-336012 and by DFG-SFB 1170. S. R. was supported by DFG-SFB 1143, DFG-SPP 1666, and by the Helmholtz association through VI-521. S. R., R. T. and N. B. P. acknowledge the hospitality of the KITP during the program “New Phases and Emergent Phenomena in Correlated Materials with Strong Spin-Orbit Coupling” and partial support by the National Science Foundation under Grant No. NSF PHY11-25915.