Pinning and I-V characteristics of a two-dimensional defective flux-line lattice

Using a variational argument, we show that a two-dimensional (2D) crystal becomes defective in the presence of a random potential. The threshold pinning force and flow properties of a plastically deformed crystal are studied using a perturbation theory valid for weak pinning potential and strong driving force. In the case of a 2D flux-line lattice, it is shown that dislocations introduce extra dissipation in the system, thus increasing the total pinning force, and resulting in nonlinear I-V characteristics.