Role of the density-of-states superconducting fluctuations in the in-plane and out-of-plane transport properties of Bi2Sr2CaCu2O8+x single crystals

We report transverse (B perpendicular to j) and longitudinal (B parallel to j) in-plane (j parallel to lab-plane) and out-of-plane (j parallel to c-axis) magnetoresistance measurements on underdoped, optimally doped and overdoped Bi2Sr2CaCu2O8+x single crystals. The measurements were performed in the temperature range from slightly above T-c to 200 K and in magnetic fields up to 13 T. The in-plane magnetoresistance (MR) is positive for all temperatures, magnetic fields and different doping levels. Near T-c, the in-plane MR is dominated by thermodynamic fluctuations, but at higher temperatures a smooth transition to the MR of normal-stale quasiparticles takes place. In sharp contrast, the out-of-plane MR is negative for all temperatures and orientations of the magnetic field. We interpret this unconventional behaviour in the framework of the superconducting fluctuation theory, taking into account different weights of the Aslamazov-Larkin and single-carrier density-of-states contributions. (C) 1999 Published by Elsevier Science B.V. All rights reserved.