Critical fields of the superconducting fullerene ${\mathrm{RbCs}}_2$${\mathrm{C}}_{60}$

The temperature dependence of the upper critical magnetic field ${\mathit{H}}_{\mathit{c}2}$ of the superconducting ${\mathrm{RbCs}}_2$${\mathrm{C}}_{60}$ fullerene has been obtained. The value of ${\mathit{H}}_{\mathit{c}2}$(0) at zero temperature is estimated to be 17 T and the coherence length ξ(0)=4.4 nm. The lower critical field ${\mathit{H}}_{\mathit{c}1}$ has been studied using three different methods. The ${\mathit{H}}_{\mathit{c}1}$(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 ${\mathit{H}}_{\mathit{c}1}$ of the superconductor. The value of ${\mathit{H}}_{\mathit{c}1}$(0) is estimated to be 5.5–8.1 mT and the penetration depth λ(0)=300–370 nm.