A quantum fluids approach to frustrated Heisenberg models

Abstract

Emphasising the close analogies between antiferromagnetism and neutral superfluidity, the authors develop a gauge-invariant quantum fluids description of non-bipartite Heisenberg systems. The antiferromagnet is treated as a spin superfluid with a rotational gauge invariance associated with the continuity of spin flow. They show how an extended Schwinger boson approach naturally incorporates the Onsager reaction fields generated by spin fluctuations, and correctly reproduces the semiclassical behaviour of spin wave theory in the large-S limit. The important short-wavelength physics of fluctuation-stabilised order is also captured by this description. For two-dimensional helimagnets at small S, the method predicts that the twist will survive the loss of sublattice magnetisation, closely analogous to the biaxial-uniaxial transition of nematic liquid crystals.