SELF-FIELD EFFECT ON CRITICAL-CURRENT DENSITY IN SINGLE-CRYSTAL BI2SR2CACU2OX

The critical current density J(c) in the a-b-plane of Bi2Sr2CaCu2Ox single crystals at 77 K has been measured for a range of angles theta between applied fields H(a) and the a-b-plane. J(c) is found to be a function of the perpendicular component H(a)perpendicular-to = H(a) sin theta only. The J(c)(H(a)perpendicular-to) curves showed a significant plateau in a low-field region, followed by a rapid drop with the increase of H(a). The critical state model of Kim et al., J(s) = alpha/(B + B0), has been modified by taking the self-field generated by the external current and demagnetization effect into account, and this modified model has described well the observed J(c) (H(a)perpendicular-to ) behavior. The implication for the roles of intrinsic pinning and extrinsic pinning on the determination of transport J(c) is discussed.