Lattice model of correlated forces in granular solids near jamming

We have devised a lattice model to study force correlations in jamming granular solids in d=2 dimensions. We perform biased Monte Carlo simulations, favoring configurations with more bonds that bear no force, to "starve" the network of bonds and thereby control the distance from the isostatic point J. Increasingly long-ranged correlations are visible as point J is approached, not in the structure of the network of force-bearing bonds but in the spatial extent of perturbations of the force magnitudes consistent with a given starved network. The correlation length so defined diverges as the isostatic point is approached as a power law with an exponent of about ξ∼δZ^-5. This divergence is much stronger than for the length scale of "soft modes" observed in jammed systems approaching point J from above.