Isotropic negative out-of-plane magnetoresistance of Bi2Sr2CuO6+delta single crystals

In the normal state, the out-of-plane resistivity rho(c) of high-quality Bi 2Sr2CuO6+delta single crystals shows an anomalously large negative magnetor esistance in magnetic fields up to 28 T. This phenomenon corresponds to a s uppression of the increase in rho(c) with decreasing temperatures as observ ed in high-T-c superconductors above the critical temperature T-c. In contr ast to the magnetoresistance in the superconducting state, this normal-stat e out-of-plane magnetoresistance is independent of the field orientation (p erpendicular and parallel to the CuO planes). This isotropic response point s to the importance of spin effects on the pseudogap in the normal state, w hereas the highly anisotropic response of the superconducting state is due to orbital effects.