Excitations of ellipsoid packings near jamming

We study the vibrational modes of three-dimensional jammed packings of soft ellipsoids of revolution as a function of particle aspect ratio e and packing fraction. At the jamming transition for ellipsoids, as distinct from the idealized case using spheres where epsilon=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 vertical bar epsilon-1 vertical bar increases. Quite surprisingly, as this new band is separated from zero frequency by a gap, and lies below the onset frequency for translational vibrations, omega*, 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, omega* depends solely on coordination as it does for compressed packings of spheres. We also discuss the regime of large vertical bar epsilon-1 vertical bar, where the two bands merge. Copyright (C) EPLA, 2009