In-plane and out-of-plane magnetoresistance in Bi2Sr2CaCu2O8+x with various carrier densities

The in-plane and out-of-plane magnetoresistance of Bi2Sr2CaCu2O8+x single c rystals was investigated in magnetic fields of 12 T, oriented parallel to t he c axes. Crystals with different carrier concentrations, corresponding to the underdoped, optimally doped, and overdoped region of the phase diagram of high-temperature superconductors, were prepared by variation of the oxy gen content. Above the critical temperature, the magnetoresistance is posit ive for in-plane and negative for out-of-plane currents in all samples. Wit h recent theories for superconducting order-parameter fluctuations, the in- plane magnetoresistance can be described well for all samples. Only the out -of-plane nzagrzetoresistance of the underdoped crystal shows distinct devi ations from the theoretical predictions and appears to be influenced by the 'pseudo-gap'.