Susceptibility and Triplet Excitation Spectrum for CaV_<b>4</b>O_<b>9</b>: Third-Order Perturbation Expansions

Abstract

The uniform susceptibility and triplet excitation spectrum of the Heisenberg antiferromagnet on the one-fifth depleted square lattice are calculated using the third-order perturbation expansion method from the viewpoint of the weakly coupled meta-plaquette picture. Both the susceptibility and triplet excitation spectrum data for CaV 4 O 9 are simultaneously explained. The origin of the relatively large spin gap in this compound is discussed.