  We report inelastic light scattering experiments on superconductor
Ce0.6Y0.4FeAsO0.8F0.2 from 4K to 300K covering the superconducting transition
temperature Tc ~ 48.6K. A strong evidence of the superconductivity induced
phonon renormalization for the A1g phonon mode near 150 cm-1 associated with
the Ce/Y vibrations is observed as reflected in the anomalous red-shift and
decrease in the linewidth below Tc. Invoking the coupling of this mode with the
superconducting gap, the superconducting gap (2) at zero temperature is
estimated to be ~ 20 meV i.e the ratio is ~ 5, suggesting Ce0.6Y0.4FeAsO0.8F0.2
to belong to the class of strong coupling superconductors. In addition, the
mode near 430 cm-1 associated with Ce3+ crystal field excitation also shows
anomalous increase in its linewidth below Tc suggesting strong coupling between
crystal field excitation and the superconducting quasi-particles. Our
observations of two high frequency modes (S9 and S10) evidence the
non-degenerate nature of Fe2+ dxz/yz orbitals suggesting the electronic
nematicity in these systems.
