Phases and phase transitions of a perturbed Kekulé-Kitaev model

Abstract: We study the quantum spin liquid phase in a variant of the Kitaev model where the bonds of the honeycomb lattice are distributed in a Kekul\'e pattern. The system supports gapped and gapless Z_2 quantum spin liquids with interesting differences from the original Kitaev model, the most notable being a gapped Z_2 spin liquid on a Kagome lattice. Perturbing the exactly solvable model with antiferromagnetic Heisenberg perturbations, we find a magnetically ordered phase stabilized by a quantum `order by disorder' mechanism, as well as an exotic continuous phase transition between the topological spin liquid and this magnetically ordered phase. Using a combination of field theory and Monte-Carlo simulations, we find that the transition likely belongs to the 3D-XYxZ_2 universality class.