High-pressure optical study of f-d hybridization in U x La1-x S single crystals

The optical reflectivity of U x La1-x S single crystals has been measured in a diamond-anvil cell for pressures up to 40 GPa. From a fit of the reflectivity spectra with one Drude term and three Lorentz oscillators the energies, intensities and widths of optical transitions are derived. In contrast to the expectation in an itinerant picture, the plasma frequencies decrease with increasing pressure, indicating the dominance of f-d hybridization effects. The non-monotonic variation with x of the plasma frequencies and the oscillator strengths of interband transitions supports the model of the simultaneous presence of localized and itinerant 5f states in U x La1-x S