Phase Diagram and Quantum Order by Disorder in the Kitaev K1 − K2 Honeycomb Magnet
journal contributionposted on 06.08.2018, 16:25 authored by Ioannis RousochatzakisIoannis Rousochatzakis, Johannes Reuther, Ronny Thomale, Stephan Rachel, Natalia B. Perkins
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.
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.