Coupling strength in superconducting fullerenes

The coupling strength λ and the characteristic phonon frequency 〈${\mathrm{\Omega }}^2$${\mathrm{〉}}^{1/2}$ in superconducting fullerenes can be determined based on general expressions for ${\mathit{T}}_{\mathit{c}}$ and on the isotope effect and NMR experimental data. An analysis of recent data shows that the superconducting state of doped fullerenes ${\mathit{A}}_3$${\mathrm{C}}_{60}$ is caused by strong electron-vibrational coupling with ${\lambda }_1$=2.1 for A=Rb and ${\lambda }_2$=1.5 for A=K, and 〈${\mathrm{\Omega }}^2$${\mathrm{〉}}^{1/2}$≃250 ${\mathrm{cm}}^{\mathrm{-}1}$.