Exotic continuous quantum phase transition between Z2 topological spin liquid and Neel order

Recent numerical simulations with different techniques have all suggested the existence of a continuous quantum phase transition between the Z(2) topological spin-liquid phase and a conventional Neel order. Motivated by this numerical progress, we propose a candidate theory for such Z(2)-Neel transition. We first argue on general grounds that, for a SU(2)-invariant system, this transition can not be interpreted as the condensation of spinons in the Z(2) spin-liquid phase. Then, we propose that such Z(2)-Neel transition is driven by proliferating the bound state of the bosonic spinon and vison excitation of the Z(2) spin liquid, i.e., the so-called (e, m)-type excitation. Universal critical exponents associated with this exotic transition are computed using 1/N expansion. This theory predicts that at the Z(2)-Neel transition, there is an emergent quasi-long-range power-law correlation of columnar valence bond solid order parameter.