Critical currents of type ii superconductors in non-transversal magnetic fields

Abstract

The force on flux lines near narrow defects elongated in the direction of the transport current is calculated. This force, together with the maximum interaction forcek _m on the central flux line element, gives the volume pinning forceF _p on the flux line lattice. The dependence ofk _m (and of the critical current densityj _c ) on the angle ϕ between the magnetic field and the transport current is calculated for different defect dimensions (with respect to the coherence length of the superconductor) and compared with the experimental results. We obtainj _c ∼sin⁻ⁿ ϕ, where 1≦≦n≦3 in dependence on the defect dimensions and on the angle interval. The possibility of testing theF _p ∼k ²_m dependence of the statistical theory of pinning is proposed.