Force-displacement characteristic of fluxoids along the c-axis in superconducting Bi-2212 single crystal near the peak field

Force-displacement characteristic of fluxoids in a superconducting Bi-2212 single crystal was measured by using the Campbell method at low temperatures and low magnetic fields where the peak effect of critical current density was observed. It is found that the interaction distance, d i , has a peak around the peak field while the Labusch parameter, α L , increases monotonously with increasing magnetic field. The peak of d i means an increment of flexibility of fluxoids to randomly distributed pins and this is considered to be brought about by some deformation of fluxoid cores along the length. Although this may be associated with the cross-over from three-dimensional flux lines to two-dimensional pancakes, the characteristic length of deformation is considered to be much longer than the distance between the CuO 2 planes.