Phases of the Chiral-Heisenberg Kagome Antiferromagnet*

The ground state degeneracy of the classical kagome Heisenberg antiferromagnet (KHAFM) is remarkably similar to that of the kagome chiral model (KCM) whose Hamiltonian consists of the scalar spin chiralities on the triangles of the lattice. However, models containing both types of interactions have reduced degeneracies. If chiral terms are introduced uniformly, the √3×√3 state lifts from the ground state manifold, but if they are introduced with staggered sign, the q=0 state is excluded instead. Only once the Heisenberg terms are entirely eliminated are states of both types again ground states. This has drastic effects on the order-by-disorder mechanism that drives coplanar ordering in the KHAFM. Our Monte Carlo simulations demonstrate a more discriminating selection effect in the intermediate models. Furthermore, even in the case of the pure KCM, only the √3×√3 structure is observed. We explain this by counting the soft modes of the KCM’s ground states. Only states of √3×√3 structure have sufficient populations of soft modes to drive the system to order. Due to an extra degeneracy of the KCM this structure exists on a large set of states forming a classical spin liquid.