BOSONIC MEAN-FIELD THEORY OF THE SPIRAL PHASES OF HEISENBERG ANTIFERROMAGNETS ON A CHAIN

We develop a bosonic mean-field theory to describe the spiral phases of a Heisenberg antiferromagnet on a one-dimensional chain, in terms of three bosons at each site. The ground state is disordered, and for large values of the spin S, two different and exponentially small energy gaps are found. The spin-spin correlation function is computed and is shown to decay exponentially at large distances. Our mean-field theory is also shown to be exact in a large-N generalization.