Intermediate-valent SmB6and the hybridization model: An optical study

Reflectivity measurements in the far-infrared region at 4 K show that the Sm${\mathrm{B}}_6$ spectrum is semiconductorlike with a reflectivity maximum located at 5.5 meV. This peak is absent at 300 K and the spectrum is metal-like. Optical constants are calculated by means of the Kramers-Kronig relations; the dielectric constants are unusually large and yield at 4 K a gap value of 3-4.7 meV. A two-oscillator fit of ${\epsilon }_2$ has been calculated and the evolving oscillator strength has been used to evaluate in first approximation the interband density of states: The results are compared to the predictions of the hybridization model.