LOW-FIELD MAGNETORESISTANCE OF BI2SR2CACU2O8 SINGLE-CRYSTALS IN THE VICINITY OF T(C)

We report a systematic study of the magnetoresistance of Bi-2:2:1:2 si ngle crystals using a small transport current and in magnetic fields l ess than 1 T. A few kelvin below the transition temperature we find ex cellent agreement with the theory of superconducting order-parameter f luctuations in two-dimensional systems. The critical temperature of an isolated double CuO2 sheet is estimated at 37 K, and the field which decouples CuO2 sheets at 0.1-0.2 T. By measuring the magnetoresistance in weak applied fields it is possible to determine the presence of sm all amounts of the Bi-2:2:2:3 phase. The presence of this latter phase makes the analysis of the fluctuation-enhanced conductivity above T(c ) very complicated.