Extended Fractons and Localized Phonons on Percolation Clusters

We investigate the localization behavior of vibrational modes of infinite percolation clusters above the critical concentration in two and three dimensions using the method of level statistics. We find that all eigenstates are localized in d=2, including the low frequency phonon states. In d=3 we obtain evidence for a localization-delocalization transition. But contrary to the common view this transition occurs for frequencies above the phonon fracton crossover giving rise to a new regime of extended fracton states.