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 e=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 |e-1| increases. Quite surprisingly, as this new band is separated from zero frequency by a gap, and lies below the onset frequency for translational vibrations, ω*, 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, ω* depends solely on coordination as it does for compressed packings of spheres. We also discuss the regime of large |e-1|, where the two bands merge.

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