Discovery of a new topological phase in the anisotropic Kitaev model with field

The Kitaev model with anisotropic interactions on the bonds of a honeycomb lattice is a paradigmatic model for quantum spin liquids. Aside from the gapless and gapped phases of the original model, more phases are revealed by the addition of a non-perturbative magnetic field. For example, the field-induced U(1) QSL phase with isotropic bonds (Kz=K) has been studied in both theory and experiments. We explore the effects of adding a magnetic field on Kitaev interactions away from the isotropic point (Kz≠K), and discover a new gapped topological phase that has eluded detection by calculations using local order parameters (e.g. susceptibility). The topological nature of this phase is reflected in (i) the emergent ground state degeneracy and (ii) the non-trivial topological entanglement entropy.