Using a non-mean-field approach the triangular lattice S=(1/2 Heisenberg antiferromagnet with nearest- and next-nearest-neighbor coupling is shown to undergo an Ising-type phase transition into a chiral symmetry broken phase (Kalmeyer-Laughlin–like state) at small T. Removal of next-nearest-neighbor coupling introduces a local $Z_2$ symmetry, thereby suppressing any finite-T chiral order.

• Received 29 June 1989

DOI:https://doi.org/10.1103/PhysRevLett.63.2524