Modes of disorder and plastic flow of flux lines in superconductors

Signatures of plastic flow of the flux-line lattice (FLL) were observed in a narrow region of the (H,T) phase diagram for 2H-NbSe₂ superconductors. In this field regime, the system is neither a rigid lattice nor a melted fluid. A model is presented to explain this nonequilibrium plastic flow based on the static interaction energy between a moving dislocation field and a pinning center. The model accounts for the observed experimental measurements and reproduces most of its features. An explicit expression is derived for the length scale R_L=δ ^[1/(δ-γ)]ξ, where ξ is the superconducting coherence length, δ=U/kT the ratio of the pinning energy to the thermal energy and γ=Ω₀ΔB/kT. Ω₀ is the increase in the lattice volume due to the presence of single point defect and ΔB is the difference between the drag coefficient of the dislocation at the normal state and the superconducting state. This length characterizes the interaction domain where forces on the FLL’s are uniform and consequently, their velocities within that domain are correlated. © 1996 The American Physical Society.