  Dynamical conductivity spectra s(w) have been measured for a diverse range of
heavy-fermion (HF) Ce and Yb compounds. A characteristic excitation peak has
been observed in the mid-infrared region of s(w) for all the compounds, and has
been analyzed in terms of a simple model based on conduction (c)-f electron
hybridized band. A universal scaling is found between the observed peak
energies and the estimated c-f hybridization strengths of these HF compounds.
This scaling demonstrates that the model of c-f hybridized band can generally
and quantitatively describe the charge excitation spectra of a wide range of HF
compounds.
