Abstract
We study the stability region for the columnar dimer state proposed as a candidate ground state for the square-lattice quantum antiferromagnet with first- and second-neighbor antiferromagnetic couplings (- model). We use a boson representation of the spin operators suited to the perturbative expansion around a dimer ground state. At lowest order, the columnar dimer is found to be stable only at the classical critical value /=1/2. However, we show that the leading anharmonic corrections stabilize the dimerized phase in a region of a finite width around /=1/2. A comparison of the ground-state energies shows that among the possible dimerized states the columnar dimer is the most favorable candidate to separate the two ordered states in the S=1/2 antiferromagnetic with first- and second-neighbor exchange.
- Received 5 August 1991
DOI:https://doi.org/10.1103/PhysRevB.44.12050
©1991 American Physical Society