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

Rb3C60 single crystals (T-c = 31 +/- 0.5 K) have been investigated by Raman spectroscopy as a function of temperature with respect to phonon and electronic scattering. One of the intermolecular Rb - C-60 phonon s observed showed changes upon cooling below the superconducting trans ition temperature indicating a strong coupling to the electronic syste m. Special attention was given to the electronic Raman scattering cros s section of Rb3C60. A clear reduction of the scattering intensity for low frequencies has been observed below T-c. This reduction is identi fied as the opening of the superconducting energy gap for which we fin d 2 Delta/k(B)T(c) = 4.0 +/- 0.5. This value was observed for several different scattering symmetries, in agreement with the proposed s-wave superconducting order parameter. (C) 1998 Elsevier Science B.V. All r ights reserved.