Exact deconfined gauge structures in the higher-spin Yao-Lee model: a quantum spin-orbital liquid with spin fractionalization and non-Abelian anyons

The spin-S Kitaev model has recently been shown to definitely exhibit topological order with spin liquid ground states for half-integer spin, but could be trivially gapped insulators for integer spin. This interesting "even-odd" effect is largely due to the fermionic (bosonic) $\mathbb{Z}_2$ gauge charges for half-integer (integer) spin. In this Letter, we theoretically show that a spin-S Yao-Lee model (a spin-orbital model with SU(2) spin-rotation symmetry) possesses exact deconfined fermionic $\mathbb{Z}_2$ gauge charges for any spin (both integer and half integer spin), which implies a topologically-nontrivial quantum spin-orbital liquid (QSOL) ground state regardless of the value of the spin quantum number. We further study the easy-axis limit of the spin-1 Yao-Lee model which can be solved in a controlled perturbative way and show that it exhibits a gapless QSOL ground state, which can even host a non-Abelian topological order by further considering time-reversal breaking interactions to gap out the Dirac cones of the gapless QSOL.
Comment: 4.5+1 pages, 1 figure