Order-by-Disorder in a Chiral Magnet on the Kagome Lattice

Counting arguments alone are not sufficient to resolutely predict the order-by-disorder mechanism which drives coplanar ordering in the classical kagome Heisenberg antiferromagnet (KHAFM). The relationship between the dimension of the ground-state manifold as estimated by Maxwell counting and the number of soft-modes in coplanar ground-states classifies the model as marginal according to the order-by-disorder criterion established by Moessner and Chalker (Phys. Rev. B 58, 12049 (1998). We have demonstrated that the classical model consisting of scalar spin chiralities on the kagome lattice (the "kagome chiral model") has the same ground-state degeneracy as estimated by Maxwell counting, and it has a subset of ground-states in close analogy to the coplanar ground-states favored by the KHAFM. However, this new model has fewer soft-modes, and they populate a more restricted set of ground-states. We undertake Monte Carlo simulation to demonstrate that order-by-disorder in the kagome chiral model is more discriminating in its selection of states at low temperature.