Spin waves in the Frustrated Kagome Lattice Antiferromagnet   KFe3(OH)6(SO4)2
  The spin wave excitations of the ideal S=5/2 Kagome lattice antiferromagnet KFe3(OH)6(SO4)2 have been measured using high-resolution inelastic neutron scattering. We directly observe a flat mode which corresponds to a lifted "zero energy mode," verifying a fundamental prediction for the Kagome lattice. A simple Heisenberg spin Hamiltonian provides an excellent fit to our spin wave data. The antisymmetric Dzyaloshinskii-Moriya interaction is the primary source of anisotropy and explains the low temperature magnetization and spin structure. 
K. Matan, D. Grohol, D. G. Nocera, T. Yildirim, A. B. Harris, S. H.   Lee, S. E. Nagler, Y. S. Lee