Phase structure of Z2 gauge theories for frustrated antiferromagnets in two dimensions

In this paper, we study phase structure of Z2 lattice gauge theories that appear as an effective-field theory describing low-energy properties of frustrated antiferromagnets in two dimensions. Spin operators are expressed in terms of Schwinger bosons, and an emergent U 1 gauge symmetry reduces to a Z2 gauge symmetry as a result of condensation of a bilinear operator of the Schwinger boson describing a short-range spiral order. We investigated the phase structure of the gauge theories by means of the Monte Carlo simulations, and found that there exist three phases, phase with a long-range spiral order, a dimer state, and a spin liquid with deconfined spinons. Detailed phase structure and properties of phase transitions depend on details of the models