Valence-bond type approach for the pyrochlore spin system

We study the ground-state properties of the spin-1 pyrochlore antiferromagnet by applying the method of the valence-bond-solid-type spin break-up to the pyrochlore lattice. The tetrahedral spin-singlet states with E representations create the many-fold degeneracy for low lying energy states, which are lifted by some couplings. We find that the magneto-elastic couplings lead to the spontaneous lattice distortion and the inter-tetrahedral couplings stabilize the parity-broken ground state. (C) 2002 Elsevier Science B.V. All rights reserved.