Weak to strong pinning crossover
Abstract
The dissipationfree current transport in typeII superconductors with finite magnetic field is established by material defects pinning the flux lines at energetically favorable locations in the crystal. In weak collective pinning, defects compete and only fluctuations in the defect density n_{p} produce pinning. The critical current is determined by the statistical summation of competing pins and is characterized by a quadratic dependence on the defect density. On the contrary, strong pins deform the lattice and induce instabilities; the pinning energy landscape becomes multivalued, producing a nonzero average of the pinning force and a critical current linear in the defect density. We discuss the crossover from weak to strong bulk pinning, which is triggered either by increasing the strength κ ∼ e_0/ξ^2 of the defect potential (e_{0} is the potential depth and ξ is the coherence length of the superconductor) or by decreasing the effective elasticity barC of the lattice. The problem is structurally related to the Landau theory of first order phase transitions and can be analyzed within a Landau expansion of the free energy. We obtain a peak effect with a strong increase in the critical current density, j_{c} ∼ j_{0} (a_0ξ^2 n_p) (ξ^2/a_0^2) (κ/barC 1)^2, with j_{0} the depairing current density and a_0=(Φ_0/B)^1/2 the mean vortex spacing.
 Publication:

APS March Meeting Abstracts
 Pub Date:
 March 2004
 Bibcode:
 2004APS..MARS12007K