Volume 87, Number 2, July 2009
Article Number 26001
Number of page(s) 6
Section Condensed Matter: Structural, Mechanical and Thermal Properties
Published online 29 July 2009
EPL, 87 (2009) 26001
DOI: 10.1209/0295-5075/87/26001

Excitations of ellipsoid packings near jamming

Z. Zeravcic1, 2, N. Xu2, 3, A. J. Liu3, S. R. Nagel2 and W. van Saarloos1

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

received 3 April 2009; accepted in final form 6 July 2009; published July 2009
published online 29 July 2009

We study the vibrational modes of three-dimensional jammed packings of soft ellipsoids of revolution as a function of particle aspect ratio $\varepsilon $ and packing fraction. At the jamming transition for ellipsoids, as distinct from the idealized case using spheres where $\varepsilon $ = 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 $\vert\varepsilon -1\vert$ 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 $\vert\varepsilon -1\vert$, where the two bands merge.

63.50.-x - Vibrational states in disordered systems.
45.70.-n - Granular systems.
63.50.Lm - Glasses and amorphous solids.

© EPLA 2009