Optical study on heavy fermion and mixed valence in Yb4As3

Temperature dependence of the electronic structure of Yb4As3 was investigated by the observation of the reflectivity spectra in the energy range from 2 meV to 50 eV at several temperatures from 39 to 320 K. In the photon energy range below 10 meV, the temperature dependence of the spectrum can be qualitatively explained by two-band model previously proposed. An absorption band with strong temperature dependence was observed at 0.4 eV. The origin is considered to be the mixing state between unoccupied Yb3+-4f and 5d. The state is considered to be important to understand the anomalous temperature dependence of the physical properties. In the energy range above 1 eV, the spectrum does not change with the temperature. The structure of the occupied and unoccupied states near the Fermi level is clarified.