FIRST EXCITATIONS OF THE SPIN-1 2 HEISENBERG-ANTIFERROMAGNET ON THE KAGOME LATTICE/

We study the exact low energy spectra of the spin 1/2 Heisenberg antif erromagnet on small samples of the kagome' lattice of up to N = 36 sit es. In agreement with the conclusions of previous authors, we find tha t these low energy spectra contradict the hypothesis of Neel type long range order. Certainly, the ground state of this system is a spin liq uid, but its properties are rather unusual. The magnetic (Delta S = 1) excitations are separated from the ground state by a gap. However, th is gap is filled with nonmagnetic (Delta S = 0) excitations. In the th ermodynamic limit the spectrum of these nonmagnetic excitations will p resumably develop into a gapless continuum adjacent to the ground stat e. Surprisingly, the eigenstates of samples with an odd number of site s, i.e. samples with an unsaturated spin, exhibit symmetries which cou ld support long range chiral order. We do not know if these states wil l be true thermodynamic states or only metastable ones. In any case, t he low energy properties of the spin 1/2 Heisenberg antiferromagnet on the kagome' lattice clearly distinguish this system from either a sho rt range RVB spin liquid or a standard chiral spin liquid. Presumably they are facets of a generically new state of frustrated two-dimension al quantum antiferromagnets.