Rubidium-doped epitaxial C60 thin films: Synthesis and electronic transport

Epitaxial thin films of C60 have been synthesized and doped with rubidium. Above 80 K, the sample resistivity shows classic metallic temperature dependence just like that of K3C60 single crystals. However, the temperature coefficient changes sign at about 80 K, and the resistivity increases by 5% before the superconducting state near 30 K is reached. As for different samples, the zero-resistance temperature varies sharply with the sample lowest resistivity and can be fitted to a functional form of Tc0=a+b rho -5. The critical current density Jc is 103-104 A cm2at approximately= 5 K, 0 T and it is found that Jc is proportional to (1-T/T c)alpha, where alpha is in the range 1.3-2.0. Furthermore, the voltage-current characteristic of the films is very similar to that of high-Tc superconductors and remains a problem for further research on this new kind of material.