Upper Critical Fields on High Temperature Superconductivity in La-Sr-Cu-O System

Abstract
The electrical resistances of three La-Sr-Cu-O samples prepared by different methods have been measured undermagnetic fields up to 20.3 tesla between 4.2 and 50 K. The upper critical fields were determined by the midpoint of the resistive transition. The largest slope of the critical field was -2.7 T/K for a sintered sample La1.85Sr0.15CuO4. According to the Werthamer, Helfand and Hohenberg expression in the dirty limit, the upper critical field H c2(0) was estimated to be 71 T. Various superconducting and normal states properties are derived.