Normal-Incidence Reflectance, Optical Properties, and Electronic Structure of Zn

The normal-incidence reflectance of electropolished Zn single crystals has been measured from 0. 6 to 4. 0 eV at 300 and 77 ^ for the polarization vector E parallel and perpendicular to the crystallographic c axis. Optical constants are determined through Kramers-Kronig inversion using a free-electron-like extrapolation for the reflectance outside the range of measurement. Results for {₂} are compared with optical spectra recently calculated by Kasowski using the band-structure calculation of Stark and Falicov, in which the coefficients of a nonlocal pseudopotential were adjusted to fit the band structure to Fermi-surface data. The present optical data agree with theory much better than do previous oblique incidence reflectance data. As predicted by the theory, a structure in {₂} at 0. 9 eV arising from transitions along and and allowed only for Ec is observed with good agreement in shape and position in energy. For both polarizations a double peak around 1. 6-2. 1 eV is seen; its shape agrees well with a double peakaround 2. 2-2. 9 eV predicted for transitions along LH in the Brillouin zone. The discrepancy in energy can be partly understood in terms of the limited accuracy of the pseudopotential and of the fit to Fermi-surface data. Application of the sum rule to the experimental {₂} gives n₄₅₅2 for both polarizations, which indicates that the extrapolation procedure used for Kramers-Kronig analysis and the magnitudes of interband structures in {₂} obtained from experiment are reasonable. In contrast, n₄₅₅ calculated from theory suggests that the interband matrix elements are at least 10-20% too large. Temperature dependence is also discussed.