We focus on YbCu4Ag and YbCu4Au and interpret the optical conductivity
, measured from 2 meV to 6 eV at 10 and 300 K, in terms of self-consis
tent electronic structure calculations. Most of the relevant spectral
structures are interpreted as interband transitions from hybridized f-
d states below and at the Fermi level at high symmetry points. Tn part
icular, the large shoulder at about 2.4 and 2 eV in the spectrum of Yb
Cu4Au and YbCu4Ag, respectively, can be interpreted in terms of a tran
sition Gamma(4) --> Gamma(3) involving mostly d states. We also compar
e the electronic structure of YbCu4Ag with that of LuCu4Ag, to ascerta
in the influence of the f states on the conduction bands and carrier d
ensity at E(F). This allows us to draw some qualitative considerations
on the S-band hybridization in these compounds. (C) 1996 American Ins
titute of Physics.