A model for competition between 'classical' and 'quantum' percolation effects in disordered electronic systems

A simple model of a diluted lattice is proposed to discuss the interplay between classical percolation and quantum localisation effects on electronic transport properties in disordered media. 'Absent' sites act as infinite barriers, while interference effects at 'occupied' sites are assumed to be negligible at random with probability alpha . The limits alpha =0 and alpha =1 are respectively 'quantum' and 'classical' percolation. The phase diagrams of conducting and insulating phases are discussed through a small-cell position-space renormalisation group in space dimensionalities d=2 and 3; in d=2 there is crossover from 'classical' to 'quantum' percolation, while in d=3 the phase structure exhibits a multicritical point and a 'classically insulating' phase which are not present in d=2.