Using an extended version of Handscomb’s Monte Carlo method we study the spin-(1/2 quantum antiferromagnetic Heisenberg model on square lattices of various sizes. The calculated correlation length associated with antiferromagnetic order grows very rapidly as the temperature is lowered suggesting an essential singularity. Our results are consistent with those recently observed by neutron scattering done on ${\mathrm{Lo}}_2$${\mathrm{CuO}}_4$.

• Received 1 December 1987

DOI:https://doi.org/10.1103/PhysRevLett.60.840