Infrared and optical spectroscopy of alpha- and gamma-phase cerium.

We determined the optical properties of alpha- and gamma-phase Ce in the photon energy range from 60 meV to 2.5 eV using ellipsometry and grazing incidence reflectometry. We observe significant changes of the optical conductivity, the dynamical scattering rate, and the effective mass between alpha- and gamma-cerium. The alpha-phase is characterized by a Fermi-liquid frequency-dependent scattering rate, and an effective mass of about 20m(e) on an energy scale of about 0.2 eV. In gamma-Ce the charge carriers have a large scattering rate in the far infrared and a carrier mass characteristic of 5d band electrons. In addition, we observe a prominent absorption feature in alpha-Ce, which is absent in gamma-Ce.