Flow behavior of a flux line in the layered superconductor 2H-${\mathrm{NbSe}}_2$ is studied with a magnetic field parallel to the layers in the vicinity of a pronounced peak effect. A striking crossover in the current-voltage characteristics is observed as the system enters the peak regime. The results yield a nonequilibrium phase diagram where conventional depinning of an elastic medium occurs for a rigid lattice. A defective (plastic) flow instability occurs as the lattice softens, but heals at large drives. This defective flow dominates the dynamics for a very soft lattice.

• Received 12 October 1992

DOI:https://doi.org/10.1103/PhysRevLett.70.2617