Theoretical interpretation of optical conductivity of YbCu4Ag,Au

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-consistent 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 particular, the large shoulder at about 2.4 and 2 eV in the spectrum of YbCu4Au and YbCu4Ag, respectively, can be interpreted in terms of a transition Gamma(4) --> Gamma(3) involving mostly d states. We also compare the electronic structure of YbCu4Ag with that of LuCu4Ag, to ascertain the influence of the f states on the conduction bands and carrier density at E(F). This allows us to draw some qualitative considerations on the S-band hybridization in these compounds.