Negative Magnetoresistance of Bi_2Sr_2CuO_x Single Crystals in a Strong Magnetic Fields

摘要

Magnetoresistance (MR) in the out-of-plane resistivity $\rho_c$ for thenormal state of the one-layer high-quality Bi_2Sr_2CuO_x single crystals undervarious dc magnetic fields up to 28 T over the temperature region 6-100 K hasbeen measured. We observed the anomalously large negative longitudinal MR up to60%. At low temperatures the normal-state MR in contrast to the MR in mixedstate is independent of the direction of the current relatively to the fielddirection suggesting uniquely the spin dominated origin of that. The magnitudeof the MR is activated in magnetic field and temperature. We interpret theactivated form of $\rho_c$ and the negative MR in terms of 2D stackedalternating metallic and dielectric layers assuming the tunneling between CuO_2planes. If the main fluctuations inside CuO_2 planes have magnetic origin, themagnetic field suppresses these fluctuations leading to the uniform spinorientation. In this case the interlayer current will be enhanced well.