Orientational mode coupling, diffuse scattering, and the order-disorder phase transition in solid C60

Abstract

We present a theory of the orientational dynamics of solid C60 which takes into account the coupling of orientational modes belonging to various symmetries and manifolds. Mode coupling strongly enhances the transition temperature and the first order character of the structural phase change to the low temperature Pa3 structure. An improved parametrization of the intermolecular potential leads to a transition temperature which is close to the experimental value and to a satisfactory description of the crystal field. The diffuse scattering in the disordered phase is investigated and the interplay of different symmetries is discussed. The theory provides a consistent description of a broad range of experimental properties.