KAGOME HEISENBERG-ANTIFERROMAGNET - ELEMENTARY EXCITATIONS AND LOW-TEMPERATURE SPECIFIC-HEAT

The ground-state properties of the Heisenberg antiferromagnet on a kag ome lattice with further-neighbor interactions are discussed. The clas sical ground states are described as spiral phases of an equivalent sq uare lattice with a basis, and quantum fluctuations are incorporated b y means of a rotationally invariant Schwinger-boson approach. The quas iparticle dispersion relations have the correct zero-mode structure, w ithout the pathologies present in the standard spin-wave approximation . For the nearest-neighbor S = 1/2 model the theory predicts an ordere d ground state, although with a largely reduced magnetization of only 18% of the classical value. Implications of the results for the low-te mperature thermodynamics of the stacked S = 3/2 kagome antiferromagnet SrCr8-xGa4+xO19 are also discussed.