Excitations of ellipsoid packings near jamming

¹  Instituut-Lorentz, Universiteit Leiden - Postbus 9506, 2300 RA Leiden, The Netherlands
²  James Franck Institute and Department of Physics, University of Chicago - Chicago IL 60637, USA
³  Department of Physics and Astronomy, University of Pennsylvania, Philadelphia PA 19104, USA

Corresponding author: zorana@lorentz.leidenuniv.nl

Received: 3 April 2009
Accepted: 6 July 2009

Abstract

We study the vibrational modes of three-dimensional jammed packings of soft ellipsoids of revolution as a function of particle aspect ratio and packing fraction. At the jamming transition for ellipsoids, as distinct from the idealized case using spheres where ε = 1, there are many unconstrained and nontrivial rotational degrees of freedom. These constitute a set of zero-frequency modes that are gradually mobilized into a new rotational band as increases. Quite surprisingly, as this new band is separated from zero frequency by a gap, and lies below the onset frequency for translational vibrations, , the presence of these new degrees of freedom leaves unaltered the basic scenario that the translational spectrum is determined only by the average contact number. Indeed, depends solely on coordination as it does for compressed packings of spheres. We also discuss the regime of large , where the two bands merge.