Deconfinement criticality in the spatially anisotropic triangular antiferromagnet with ring exchange

The spatially anisotropic triangular antiferromagnet is investigated with the numerical diagonalization method. As the anisotropy varies, the model changes into a variety of systems such as the one-dimensional, triangular, and square-lattice antiferromagnets. Taking into account such a geometrical character, we impose the screw-boundary condition, which interpolates smoothly the one- and two-dimensional lattice structures. Diagonalizing the finite clusters with N=16,20,...,32 spins, we observe an intermediate phase between the valence-bond solid (VBS) and Néel phases. Suppressing the intermediate phase by applying the ring exchange, we realize a direct VBS-Néel transition. The simulation data indicate that the transition is a continuous one with the correlation-length critical exponent ν=0.80 (15). These features are in agreement with the deconfinement-criticality scenario advocated by Senthil and co-workers in the context of the high-temperature superconductivity.