Distribution of shielding currents in underdoped Bi-2212 single crystal

Contributions to the irreversibility from the bulk and the surface are inve stigated in detail for an underdoped Bi-2212 single crystal using the Campb ell method. The measured flux profile showed a linear fur distribution sugg esting a uniform bulk shielding current as the Bean model predicts in the f ield-temperature region far below the irreversibility line. Getting close t o the irreversibility line, the ac penetration depth became larger and woul d probably exceed the specimen size because the critical current density ap proached zero. Hence, the obtained profile was different from the exact one . However, no sign of the surface irreversibility was discovered in this sp ecimen.