Localization behavior of vibrational modes in granular packings

We study the localization of vibrational modes of frictionless granular media. We introduce a new method, motivated by earlier work on non-Hermitian quantum problems, which works well both in the localized regime where the localization length. is much less than the linear size L and in the regime xi greater than or similar to L L when modes are extended throughout our finite system. Our very lowest frequency modes show quasi-localized resonances away from the jamming point; the spatial extent of these regions increases as the jamming point is approached, as expected theoretically. Throughout the remaining frequency range, our data show no signature of the nearness of the jamming point and collapse well when properly rescaled with the system size. Using Random Matrix Theory, we derive the scaling relation xi similar to L(d/2) for the regime xi >> L in d dimensions. Copyright (c) EPLA, 2008.