PYROCHLORE ANTIFERROMAGNET - A 3-DIMENSIONAL QUANTUM SPIN LIQUID

The quantum pyrochlore antiferromagnet is studied by perturbative expa nsions and exact diagonalization of small clusters. We find that the g round state is a spin-liquid state: The spin-spin correlation function s decay exponentially with distance and the correlation length never e xceeds the interatomic distance. The calculated magnetic neutron diffr action cross section is in very good agreement with experiments perfor med on Y(Sc)Mn-2. The low energy excitations are singlet-singlet ones, with a finite spin gap.