Abstract
We propose a versatile approach to treat commonly arising constraints. It is illustrated for interacting magnons of the Heisenberg antiferromagnet on a square lattice. For systems of sites a nonperturbative continuous unitary transformation (CUT) is used to derive an effective Hamiltonian conserving the number of magnons. They are bosonic particles with a hard-core constraint which is captured by a local, repulsive interaction . The limits and are achieved by extrapolation. The residual spin gap is smaller than reflecting the gapless nature of the magnons. The one-magnon dispersion displays all known characteristics.
- Received 12 December 2005
DOI:https://doi.org/10.1103/PhysRevB.73.172407
©2006 American Physical Society