Title: Jammed Particulate Systems Are Highly Anharmonic Solids

Author (Talk): Carl Schreck, Yale University

Abstract:

We computationally study packings of bidisperse disks and spheres at the onset of jamming to assess their response to weak thermal fluctuations. We first diagonalize the dynamical matrix (DM) for the static packings to obtain the spectrum of vibrational modes. We test to what extent these systems are harmonic by perturbing them along each of the eigenmodes of the DM and decomposing the response into the original set of modes. We find that these systems are generically anharmonic: the response to the perturbation contains a continuous range of frequencies (not the original frequency) even for vanishingly short times following the perturbation. The anharmonicity arises from the finite fraction of contacts that are poised to form and break near jamming. We describe a method for calculating an effective interaction potential between particles averaged over contacts that break and reform, which may lead to a more robust set of vibrational modes and harmonic response.