Jc-B-T surface of high-Jc Bi2Sr2CaCu2O8+x/Ag tape

Critical current density Jc of an Ag-clad tape Bi2Sr2CaCu2O8+x has been studied in the temperature range 7-77 K and magnetic field B ≤ 6.5 T. For T ≥ 21 K, Jc(B) and the pinning force density Fp=JcB show scaling behaviour with the scaling field B* corresponding to the field of maximum Fp. At intermediate fields (0.5≤B/B*≤2.5) Jc ∼ exp(-B3/2), whereas well below and above B*, Jc shows the asymptotic B-α variations with α approx. 0.2 and 3 respectively. The thermally activated flux motion and the thermal smearing of the pinning potential describe equally well the temperature dependence of B* for T ≤ 70 K. These findings show that in finite fields well-prepared tape behaves as homogeneous high-Tc superconductor (HTS). The implications of these results for the understanding of Jc in HTSs and the applications of tapes are briefly discussed. (author)