First excitations of the spin 1/2 Heisenberg antiferromagnet on the kagomé latticeCh. Waldtmann, H.-U. Everts, B. Bernu, C. Lhuillier, P. Sindzingre, P. Lecheminant and L. PierreEur. Phys. J. B, 2 4 (1998) 501-507DOI: https://doi.org/10.1007/s100510050274