Commensurability effects in superconductors with bulk and intrinsic pinning

Abstract

The pinning of the flux line lattice (FLL) interacting with CuO planes and randomly distributed point defects is studied accounting for the effects related to the commensurability between the flux line and crystal lattices. The pinning by point defects is described in terms of the collective pinning model. It is shown that the interplay between pinning by point defects and the CuO planes determines the temperature and field ranges of the commensurability oscillations in the magnetic field dependence of magnetization and critical current. The Gibbs free energy of the system is calculated. The effective pinning potential caused by the FLL interaction with the point pinning sites decays with the magnetic field much faster than that originating from the CuO planes. As a result, the crossover from 3D to 2D pinning can occur with the growth of the magnetic field. It is shown that the pinning of the FLL by the system of ideal parallel planes results not only in the change in the critical current directed along the planes but produces also a pronounced effect on the transverse critical current.