SPECTRAL STATISTICS NEAR THE QUANTUM PERCOLATION-THRESHOLD

The statistical properties of spectra of a three-dimensional quantum b ond percolation system are studied in the vicinity of the metal-insula tor transition. In order to avoid the influence of small clusters, onl y regions of the spectra in which the density of states is rather smoo th are analyzed. Using the finite-size scaling hypothesis, the critica l quantum probability for bond occupation is found to be p(q)=0.33+/-0 .01 while the critical exponent for the divergence of the localization length is estimated as nu=1.35+/-0.10. This later figure is consisten t with the one found within the universality class of the standard And erson model.