Intraband and interband processes in the infrared spectrum of metallic aluminum

Abstract

The dielectric function of polycrystalline metallic aluminum derived by Shiles et al. [Phys. Rev. B 22, 1612 (1980)] from room-temperature ultrahigh-vacuum reflectance measurements has been analyzed into intraband and interband components and compared with theoretical predictions of Szmulowicz and Segall [Phys. Rev. B 24, 892 (1981)]. For this analysis, a new approach was developed, which utilizes experimental data over a larger energy range than in previous studies. To within experimental uncertainty, the resulting intraband component is consistent with a Drude model having a plasma frequency ${\Omega }_p$=12.5±0.3 eV and relaxation time τ=(1.06±0.12)×${10}^{\mathrm{-}14}$ sec. These values are in accord with the bulk static conductivity which in turn is in agreement with the inertial sum rule on the real part of the dielectric function. The interband contribution was found to consist of a broad background with two superimposed peaks: the well-known ‘‘0.8 μm’’ absorption at ∼1.5 eV and a weaker absorption in the vicinity of 0.4 eV. This interband spectrum is in good agreement in regard to both peak position and oscillator strength with the one-electron augmented-plane-wave model calculations for the optical conductivity by Szmulowicz and Segall. The total experimental intraband and interband oscillator strengths for the conduction electrons are 1.9 and 1.2 electrons/per atom, respectively.