Investigation of pinning centres in superconductors by means of alternating currents. I. Theory

The interaction between the fluxon lattice and a random array of pinning sites can be analyzed with the help of a simple model. The critical current calculated from the model corresponds to the more refined calculation of Labusch (1969). The model is used to analyse the response of a fluxon lattice to very small forces. It is shown that the displacement of the fluxon lattice is reversible and linear in the applied force up to a certain maximum displacement. Measurement of the displacement due to small forces can be performed by measuring the electric field in a slab carrying a small alternating current. Such measurements can yield useful information about pinning centres.