Self-Organized Critical Behavior in Pinned Flux Lattices

We study the response of pinned flux lattices, under small perturbations in the driving force, below and close to the pinning-depinning transition. For driving Lorentz forces below Fc (the depinning force at which the whole flux lattice slides), the system has instabilities against small force increases, with a power-law distribution characteristic of self-organized criticality. Specifically, D(d)~d^-1.3, where d is the displacement of a flux line after a very small force increase. We also study the initial stages of the motion of the lattice once the driving force overcomes the pinning forces.