Angular dependence of the upper critical field in Bi2Sr2CuO6+δ

The angular dependence of the upper critical magnetic field was investigated in a wide range of temperatures in very high-quality Bi2Sr2CuO6 + delta single crystals with critical temperature T-c (midpoint) similar or equal to 9 K in magnetic fields up to 28 T. Although the typical value of the normal state resistivity ratio rho(c)/rho(ab) approximate to 10(4), the anisotropy ratio H-c2 parallel toparallel to ab/H-c2 perpendicular to ab of the upper critical fields is much smaller and shows an unexpected temperature dependence. A model based on strong anisotropy and small transparency between superconducting layers is proposed. (C) 2002 MAIK "Nauka/Interperiodica".