Recent neutron-scattering data for the spin-correlation length in ${\mathrm{La}}_2$${\mathrm{CuO}}_4$ can be fitted quantitatively with an analysis of the quantum mechanical nonlinear σ model in two space dimensions. The coupling constant must be chosen in the range where an isolated ${\mathrm{CuO}}_2$ layer has antiferromagnetic order at T=0. The parameters are consistent with the spin-wave theory for the nearest-neighbor spin-(1/2 Heisenberg antiferromagnet on a square lattice.

• Received 24 December 1987

DOI:https://doi.org/10.1103/PhysRevLett.60.1057