OPTIMIZED RVB STATES OF THE 2-D ANTIFERROMAGNET - GROUND-STATE AND EXCITATION SPECTRUM

The Gutzwiller projection of the Schwinger-boson mean-field solution of the 2-d spin-1/2 antiferromagnet in a square lattice is shown to produce the optimized, parameter-free RVB ground state. We get -0.6688J/site and 0.311 for the energy and the staggered magnetization. The spectrum of the excited states is found to be linear and gapless near k congruent-to 0. Our calculation suggests, upon breaking of the rotational symmetry, epsilon(k) congruent-to 2JZ(r) square-root 1 - gamma(k)2 with Z(r) congruent-to 1.23.