Longitudinal elastic correlation length of flux lines along the c-axis in superconducting Bi-2212 single crystal

The longitudinal elastic correlation length, l(44), of flux lines along the c-axis is measured using the Campbell method with the magnetic field parallel to the c-axis for a superconducting Bi-2212 single crystal. It is found that l(44) is of the order of 10 mu m and four orders of magnitude longer than the distance between the CuO2 planes. In addition, l(44) increases with increasing magnetic field and/or temperature. These results agree well with the theoretical estimate of the pinning correlation length using the observed critical current density. The apparent pinning potential associated with the magnetic relaxation rate is calculated using these results and compared with the experimental result. Agreement is satisfactory. It is also found that the transverse flux-bundle size is as short as the flux-line spacing. It is concluded from these results that the flux lines are rather one-dimensional and strongly coupled along the c-axis.