Optical Properties of Single-Crystal Zinc

Measurements were made of the absorptivity of single crystals of zinc from 0.1 to 3.0 eV at 4.2K. Polarized radiation was used with the electric field vector parallel or perpendicular to the $c$ axis of the crystal. New structure was found for $\overrightarrow{\mathrm{E}}\perp \hat{c}$ at about 0.15 eV; no low-energy structure was observed for $\overrightarrow{\mathrm{E}}\parallel \hat{c}$. The low-energy interband transition is attributed to transitions near the point $K$ in the Brillouin zone. The structure in the near-infrared and visible spectra is highly temperature dependent. Comparisons of the absorptivity and the conductivity are made between our 4.2-K data and the data of Rubloff for 77 and 300 K and with the calculations of Kasowski. Thermomodulation measurements on basal-plane samples are described which show the conductivity doublet as originating from two distinct infrared-absorption structures. The low-energy absorptivity is found to be nearly constant for $\overrightarrow{\mathrm{E}}\parallel \hat{c}$. An optical effective-mass component $m_{\parallel }^{*}$ of 2.$0m_0$ is computed from theories of the anomalous skin effect.