Testing for Z2 topological order in variational wave functions for spin liquids -: art. no. 094421

We determine the conditions under which a spin-liquid Mott insulator \0] defined by a Gutzwiller projected BCS state at half-filling is Z(2) fractionalized. We construct a trial vison (Z(2) vortex) state \V) by projecting an hc/2e vortex threading the hole of a cylinder/torus and examine its overlap with \0) using analytical and numerical calculations. We find that generically the overlap vanishes in the thermodynamic limit, so the spin-liquid is Z(2) fractionalized. We point out the relevance of these results to numerical studies of Hubbard-like models and spin models which have been recently reported to possess spin liquid phases. We also consider possible implications for flux-trapping experiments that have tested for Z(2) fractionalization in underdoped high-temperature superconductors.