Resonating-Valence-Bond Ground State of CaV₄O₉ Studied by the Gutzwiller-Projected Schwinger-Boson Method

Abstract

An antiferromagnetic Heisenberg model on a 1/5-depleted two-dimensional square lattice, a model of CaV_4O_9, is investigated by variational Monte Carlo simulation.A prototype of a trial wave function is obtained byprojecting out the doubly occupied statesfrom the Schwinger-boson mean-field solution.Then variational Monte Carlo simulation is performed forup 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, the staggered magnetization, static structure factor, andexcitation spectrum are calculated.It is shown that the Néel order survives and there is no gapat isotropic coupling.