Dynamical Conductivity and Plasmon Excitation in Bi

The reflectivity of bismuth crystals is measured in the spectral range 50 to 500 cm−1. From the measured data the dielectric function is determined by a'Kramers‐Kronig analysis. The dispersion of this function is explained by the dynamical conductivity of a free electron gas. At frequencies above the plasma edge there is a contribution which is due to the excitation of plasmons by the interaction of the free electrons with the Coulomb fields of impurities. This contribution can be expected from model calculations of the dynamical conductivity, considering ionized impurity scattering and screening effects.