ON THE QUANTUM KAGOME ANTIFERROMAGNET

The purpose of the present paper is to review investigations of the an tiferromagnetic Heisenberg model on the kagome lattice and to propose some schemes based on the spin-wave theory by which physical propertie s of the present model can be better understood. By means of our schem es, it is shown that the linear-spin-wave fiat mode of the present mod el comes from the semi-local symmetry of the linear-spin-wave Hamilton ian, where the flat mode has an excitation-spectrum with omega = 0 for all k. It is also shown that the inclusion of higher-order quantum fl uctuations may break the symmetry and thereby the hat mode may be lift ed up.