Resonating-Valence-Bond Ground-state of CaV4O9 Studied by the Gutzwiller-projected Schwinger-boson method

An antiferromagnetic Heisenberg model on a 1/5-depleted two-dimensional square-lattice, a model of CaV4O9, is investigated by variational Monte Carlo simulation. A prototype of a trial wave function is made by projecting out the doubly occupied states from the Schwinger-boson mean-field solution. Then variational Monte Carlo simulation is performed up to 40× 40 sites(including 320 vacant sites). The optimized state has the lowest energy, −0.5510J , ever reported. For this state energies of a dimer bond and a plaquette bond, staggered magnetization, static structure factor, and excitation spectrum are calculated. It is shown that the Néel order survives and there is no gap at isotropic coupling. 75.10.-b, 75.10.Jm, 75.50.Ee Typeset using REVTEX