Spin-1/2 frustrated antiferromagnet on a spatially anisotropic square lattice: Contribution of exact diagonalizations

The phase diagram of a spin-1/2 J-J(')-J(2) model is investigated by means of exact diagonalizations on finite samples. This model is a generalization of the J(1)-J(2) model on the square lattice with two different nearest-neighbor couplings J,J(') and may also be viewed as an array of coupled Heisenberg chains. The results suggest that the resonating valence bond state predicted by Nersesyan and Tsvelik [Phys. Rev. B 67, 024422 (2003)] for J(2)=0.5J(')