CRITICAL FIELDS OF THE SUPERCONDUCTING FULLERENE RBCS2C60

The temperature dependence of the upper critical magnetic field H-c2 of the superconducting RbCs2C60 fullerene has been obtained. The value of H-c2(0) at zero temperature is estimated to be 17 T and the coherence length zeta(0)=4.4 nm. The lower critical field H-c1 has been studied using three different methods. The H-c1(T) dependence obtained from the procedures based on the deviation from perfect diamagnetism and on Bean's critical-state model has a positive curvature with decreasing temperature. It is shown from a high-field analysis that this saturationless dependence does not reflect the intrinsic H,, of the superconductor. The value of H-c1(0) is estimated to be 5.5-8.1 mT and the penetration depth lambda(0)=300-370 nm.