Upper critical field from normal state fluctuations in Bi2Sr2CuO6+δ

The in-plane magnetoresistance of an epitaxial Bi2Sr2CuO6+delta thin film was systematically investigated as a function of doping, above T-c. The orbital magnetoconductance is used to extract the crossover field line H-c2(*)(T) in the fluctuation regime. This field is found in good agreement with the upper critical field obtained from resistivity data below T-c, and exhibits a similar upward curvature, thus pointing toward the existence of a critical correlation length. The consequences regarding the nature of the resistive transition are discussed.