EVIDENCE FOR JAHN-TELLER COUPLING AND FANO RESONANCE OF LOWER <font>H</font><font>g</font> MODES IN <font>K</font>3<font>C</font>60 AND <font>Rb</font>3<font>C</font>60 FILMS FROM RAMAN SCATTERING

The Raman scattering study of superconducting thin films of A 3 C 60 (A=K,Rb) carried out upon laser excitations at 1.16 and 2.41 eV have revealed the significant broadening and Fano-lineshapes of several low energy H g intramolecular modes with relative intensities and widths depending on excitation energies. The most interesting feature of the 1.16 eV excited spectrum is the wide asymmetric band at 400 cm −1 which can be assigned by Fano-shape fitting to enormously broadened H g (2) mode red shifted compared to its bare frequency of 408 cm −1. The narrowing of all lower H g modes in insulating A 6 C 60 phase indicates strong electron-phonon coupling of this Jahn-Teller modes in x =3 phase and suggests that this low energy vibrations are contributing to superconducting pairing. However the possibility to interpret the wide band at 400 cm −1 as the maximum of electronic background can not be ruled out yet and is supported by our preliminary observations of its disappearance at low temperature below T c .