WEAKLY FRUSTRATED SPIN-1/2 HEISENBERG-ANTIFERROMAGNET IN 2 DIMENSIONS - THERMODYNAMIC PARAMETERS AND THE STABILITY OF THE NEEL STATE

Using a Schwinger-boson mean-field theory, we calculate the low-temperature uniform transverse susceptibility chi(perpendicular-to) and spin-wave velocity c for the weakly frustrated spin-1/2 square-lattice Heisenberg antiferromagnet with exchange couplings J1, J2, and J3 to first, second, and third neighbors. By connecting chi(perpendicular-to) and c to the bare coupling of the nonlinear a model that describes the long-wavelength limit of the antiferromagnet, we are able to improve upon earlier renormalization-group estimates of the zero-temperature phase boundary separating Neel and magnetically disordered ground states. To one-loop level in an epsilon expansion we find a disordering transition across a line joining the points (J2,J3)/J1=(0.15,0) and (0,0.09). Thus, the classical phase boundary (J2+2J3)/J1=1/2 is shifted asymmetrically by quantum fluctuations, as expected when the transition is to a columnar dimerized ground state.