Numerical evidences of fractionalization in an easy-axis two-spin Heisenberg antiferromagnet

Based on exact numerical calculations, we show that the generalized kagome spin model in the easy-axis limit exhibits a spin liquid, topologically degenerate ground state over a broad range of phase space, including a point at which the model is equivalent to a Heisenberg model with purely two-spin exchange interactions. We further present an explicit calculation of the gap (and dispersion) of "vison" excitations, and exponentially decaying spin and vison two-point correlators. These are hallmarks of deconfined, fractionalized, and gapped spinons. The nature of the phase transition from the spin-liquid state to a magnetic ordered state tuned by a negative four-spin "potential" term is also discussed in light of the low energy spectrum. These results greatly expand the range and the theoretical view of the spin-liquid phase in the vicinity of the Rokhsar and Kivelson exactly soluble point.