On variational arguments for vibrational modes near jamming

¹ Kavli Institute for Theoretical Physics, University of California - Santa Barbara, CA 93106, USA
² Institute of Theoretical Physics, École Polytechnique Fédérale de Lausanne - CH-1015 Lausanne, Switzerland

^(a) lyan@kitp.ucsb.edu
^(b) matthieu.wyart@epfl.ch

Received: 14 February 2016
Accepted: 4 May 2016

Abstract

Amorphous solids tend to present an abundance of soft elastic modes, which diminish their transport properties, generate heterogeneities in their elastic response, and affect non-linear processes like thermal activation of plasticity. This is especially true in packings of particles near their jamming transition, for which effective medium theory and variational arguments can both predict the density of vibrational modes. However, recent numerics support that one hypothesis of the variational argument does not hold. We provide a novel variational argument which overcomes this problem, and correctly predicts the scaling properties of soft modes near the jamming transition. Soft modes are shown to be related to the response to a local strain in more connected networks, and to be characterized by a volume , where is the excess coordination above the Maxwell threshold. These predictions are verified numerically.