title: Disordered surface vibrations in jammed sphere packings.
abstract: We study the vibrational properties near a free surface of disordered spring networks derived from jammed sphere packings. In bulk systems, without surfaces, it is well understood that such systems have a plateau in the density of vibrational modes extending down to a frequency scale ω*. This frequency is controlled by ΔZ = 〈Z〉 - 2d, the difference between the average coordination of the spheres and twice the spatial dimension, d, of the system, which vanishes at the jamming transition. In the presence of a free surface we find that there is a density of disordered vibrational modes associated with the surface that extends far below ω*. The total number of these low-frequency surface modes is controlled by ΔZ, and the profile of their decay into the bulk has two characteristic length scales, which diverge as ΔZ(-1/2) and ΔZ(-1) as the jamming transition is approached.
authors.affiliation: Department of Physics and Astronomy, University of Pennsylvania, 209 South 33rd Street, Philadelphia, Pennsylvania 19104, USA. dsussman@sas.upenn.edu.
authors.forename: Daniel M
authors.initials: DM
authors.lastname: Sussman
authors.forename: Carl P
authors.initials: CP
authors.lastname: Goodrich
authors.forename: Andrea J
authors.initials: AJ
authors.lastname: Liu
authors.forename: Sidney R
authors.initials: SR
authors.lastname: Nagel