Spin correlation functions and N\'{e}el order in the 2D Heisenberg model: Effects of spatial anisotropy

The ground-state properties of the square-lattice spin-1/2 Heisenberg antiferromagnet with spatially anisotropic couplings are investigated by Green's-function projection approaches. The staggered magnetization and the two-spin correlators are calculated; the competition between magnetic long- and short-range order is discussed in comparison with experiments on $\rm Sr_2[Ca_2]CuO_3$.