SUPERCONDUCTING FLUCTUATION EFFECTS ON THE MAGNETOCONDUCTIVITY IN SINGLE-CRYSTALLINE YBA2CU3O7-DELTA AND BI2SR2CACU2O8+DELTA

Precise resistivity measurements in magnetic fields up to 6 T have been performed on single crystalline YBa2Cu3O7-delta and Bi2Sr2CaCu2O8+delta samples. The results show that the resistivity change becomes anomalously broad over a wide temperature region around T(c), in both cases in a similar fashion; the broadening is most significant when the magnetic field is applied along the crystallographic c-axis, irrespective of the relative orientation between the current and the magnetic field. This behavior is discussed in the superconducting fluctuation model and associated with the extremely short coherence length in highly two dimensional nature of the electronic structure. The broadening cannot be ascribed to the traditional Lorentz force driven mechanisms such as flux flow and flux creep models.