Quantum Loop States in Spin-Orbital Models on the Honeycomb Lattice

Abstract

We construct a physically realistic and analytically tractable model for spin-1 systems with orbital degeneracy on the honeycomb lattice, relevant to honeycomb materials with large Hund's and weak spin-orbit couplings, and two electrons in t2g orbitals. This model realizes many new phases whose building blocks are orbital loops decorated by Haldane chains. These include a Haldane loop crystal, a symmetry-protected topological phase, and, notably, a regime where the decorated loops resonate. When taken to the three-dimensional hyperhoneycomb lattice, the latter regime becomes a (symmetry-enriched) U(1) quantum spin-orbital liquid, "disordered" both in the spin and orbital channels. We hope this construction will pave the way for realizing many of the Haldane-chain-based phases which have been theoretically proposed in the literature.