DETERMINATION OF THE SUPERCONDUCTING ENERGY-GAP OF RB3C60 BY RAMAN-SCATTERING

Pure C-60 and Rb3C60 (T-c=28K) have been investigated by Raman spectro scopy as a function of temperature (2.2-300K) with respect to phonon a nd electronic scattering. All measurements were performed on powder sa mples using laser intensities below 4W/cm(2) and O-2-free conditions. The temperature dependence of the frequency and line shape of several phonons was investigated near T-c. Special attention was given to the electronic Raman scattering cross section of Rb3C60, which was found t o be smaller (approximate to 1/5) compared with cuprate superconductor s, e.g., Bi-2212. Tn normalized spectra (I-4.2K/I-31K) for temperature s below and above T-c a clear reduction of the scattering intensity wa s observed for frequencies below about 150cm(-1). This reduction is id entified as the superconducting energy gap with 2 Delta/k(B)T(c)=7.7+/ -1.1.