Scaling function for the spin correlation length in the two-dimensional quantum nonlinear sigma model

The scaling function for the spin correlation length xi of the two-dimensional (2D) quantum nonlinear sigma model is obtained by Monte Carlo simulations. This is used to extract the temperature dependence of the spin correlation length, which sheds light on the nature of the ground state of low-dimensional quantum antiferromagnets. A crossover from quantum critical to renormalized classical behavior of the correlation length is found. Comparison is made with numerical results on the 2D square lattice Heisenberg model, as well as with neutron-scattering and nuclear magnetic relaxation experiments.