ON THE QUANTUM KAGOMÉ ANTIFERROMAGNET

Abstract
The purpose of the present paper is to review investigations of the antiferromagnetic Heisenberg model on the kagomé lattice and to propose some schemes based on the spin-wave theory by which physical properties of the present model can be better understood. By means of our schemes, it is shown that the linear-spin-wave flat mode of the present model comes from the semi-local symmetry of the linear-spin-wave Hamiltonian, where the flat mode has an excitation-spectrum with ω≡0 for all k. It is also shown that the inclusion of higher-order quantum fluctuations may break the symmetry and thereby the flat mode may be lifted up.

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