Thermal features of Heisenberg antiferromagnets on edge- versus corner-sharing triangular-based lattices: A message from spin waves

Abstract

We construct modified spin-wave thermodynamics for frustrated noncollinear antiferromagnets for the first time. The well-known modified spin-wave theory for collinear antiferromagnets diagonalizes a bosonic Hamiltonian subject to the constraint that the total staggered magnetization be zero. Applying this scheme as it is to frustrated noncollinear antiferromagnets ends in a poor thermodynamics, missing the optimal ground state and breaking the local U(1) rotational symmetry. We find a new double-constraint modification scheme to overcome this difficulty, which is tuned especially to frustrated spiral magnets but spontaneously goes back to the standard single-constraint condition at the onset of a collinear N\'eel-ordered classical ground state. We apply this new scheme to triangular-based polyhedral and planar antiferromagnets with particular interest in a possible contrast between edge- versus corner-sharing geometries. Under such circumstances that very few methods are available to calculate finite-temperature properties of frustrated noncollinear quantum magnets in the thermodynamic limit, our newly developed modified spin-wave theory predicts that the specific heat of the kagome-lattice Heisenberg antiferromagnet in the corner-sharing geometry remains having both mid-temperature broad maximum and low-temperature narrow peak in the thermodynamic limit, while the specific heat of the triangular-lattice Heisenberg antiferromagnet in the edge-sharing geometry retains a low-temperature sharp peak followed by a mid-temperature weak anormaly in the thermodynamic limit.