HUGE MAGNETIC ENHANCEMENT OF THE OUT-OF-PLANE RESISTIVITY AND DEPRESSION OF T-C ONSET IN BI-2212 SINGLE-CRYSTAL

During magnetoresistance measurement of Bi-2212 single crystals, we fo und the resistance in the c-axis direction exhibited a huge magnetic e nhancement (H perpendicular to the a-b-plane) while the onset transiti on temperature along the c-axis showed a large depression when the mag netic fields were over a certain value (H > 180 Oe). No such phenomena were observed in small applied magnetic fields (H less than or equal to 180 Oe) and in a-b-plane magnetoresistance measurements. By changin g different probes (eight probes being attached to the sample, each si de having four probes) for the measurement of the magnetoresistance al ong the c-axis with H = 2000 Oe, we found that the resistance along th e c-axis in the temperature region T/T-c > 0.90 was only related to th e measuring dimensions and T-c onset remained unchanged. Our results p rovided evidence that both Lorentz-force-independent fluctuation-induc ed dissipation and Lorentz-force-dependent vortex motion dissipation e xist in the mixed state.