Spin Dynamics of Trimers on a Distorted Kagom\'e Lattice

We treat the ground state, elementary excitations, and neutron scattering cross section for a system of trimers consisting of three tightly bound spins 1/2 on a distorted Kagom\'e lattice, subject to isotropic nearest neighbor (usually antiferromagnetic) Heisenberg interactions. The interactions between trimers are assumed to be weak compared to the intra trimer interactions. We compare the spin-wave excitation spectrum of trimers with that obtained from standard spin-wave theory and attribute the differences at low energy to the fact that the trimer formulation includes exactly the effects of intra-trimer zero point motion. Application to existing systems is briefly discussed.