EFFECTIVE-MEDIUM THEORY FOR THE NORMAL-STATE IN ORIENTATIONALLY DISORDERED FULLERIDES

An effective medium theory for studying the electronic structure of th e orientationally disordered M3C60 fullerides is developed and applied to study various normal state properties. The theory is based on a cl uster-Bethe-lattice method in which the disordered medium is modeled b y a three-band Bethe lattice, into which we embed a molecular cluster whose scattering properties are treated exactly. Various single-partic le properties and the frequency-dependent conductivity are calculated in this model, and comparison is made with numerical calculations for disordered lattices, and with experiment.