Anisotropic Optical Properties of Heavy-Rare-Earth Single Crystals

The optical absorptivities of oriented single crystals of hcp Gd, Tb, Dy, Ho, Er, Tm, and Lu were measured at 4.2 K between 0.2 and 4.4 eV. Polarized radiation was used to reveal the optical anisotropy. Systematic movement of structures in the absorptivity and optical conductivity was observed as a result of trends within sp and d bands. Low-energy structures were related to effects of s−f exchange interaction, but were more complicated than previously thought

Absorptivity of Single-Crystal Yttrium at 4.2 K

Measurements of the absorptivity of single crystals of Y were made between 0.15 and 4.4 eV at 4.2 K. Polarized radiation was used with the electric vector parallel or perpendicular to the c^ axis of the crystal. The observed structures in the absorptivity were interpreted on the basis of band calculations for Sc, Re, and Gd and qualitative agreement was found between the band structures and the observed spectra

Optical Properties of Single-Crystal Cadmium

Measurements were made of the reflectivity and/or absorptivity of cadmium from 0.15 to 20 eV, using polarized light with the electric vector both perpendicular and parallel to the c axis of the crystal. In the visible and infrared spectra both polarizations yielded strong absorption peaks. For perpendicular polarization, the main peak was at 0.98 eV and was attributed mainly to transitions between bands along the L−H symmetry line. Also in this polarization there was an absorption edge at 0.29 eV. This may be due to transitions near the point K in the Brillouin zone. For parallel polarization, the main absorption peak was at 1.10 eV and was attributed to transitions between bands along Γ−K, Γ−M, and L−H. No low-energy absorption edge was found for parallel polarization. Agreement between the experimental data and the calculations of Kasowski based on a nonlocal-pseudopotential model was fairly good. There was no agreement between the data and calculations based on a local-pseudopotential model. At low temperatures, the long-wavelength absorptivities were approximately constant, in agreement with theory for the anomalous-skin-effect region. Using the theory of Kliewer and Fuchs and the experimental data, parallel and perpendicular effective masses were calculated to be 1.09m0 and 1.61m0, respectively. The weighted average of these is in good agreement with the thermal effective mass for cadmium. The low-energy data support the theory of Kliewer and Fuchs and tend to confirm the volume absorption process suggested by Holstein

Multiplet Structure below Threshold in Appearance-Potential Spectra—Lanthanum N4,5

We present the N4,5 appearance-potential spectrum of La. Structure exists at energies lower than the threshold energy for transitions terminating at the Fermi level. Several similarities between optical absorption spectra and our results are discussed. These results contradict the simple model usually used to interpret appearance-potential spectra and emphasize the need for a new theory

Optical properties of Ti, Zr, and Hf from 0.15 to 30 eV

The absorptivity or reflectivity of polycrystalline samples of Ti, Zr, and Hf was measured from 0.15 to ∼30 eV. The data were Kramers-Kronig analyzed to determine the dielectric functions. Between ∼0.2 and ∼7 eV, each metal showed five structures in the absorptivity and ε2. These were interpreted as interband transitions within the d bands. The ε2 spectra had minima near 7 eV similar to that observed in the bcc transition metals. Additional structures at higher energy could be related to transitions involving highlying bands and the core levels. The electron-energy-loss functions were calculated and discussed in terms of volume and surface plasmons. These metals, like the other transition metals studied, exhibited two volume and two surface plasmons

Soft-x-ray appearance potential spectra of La and Ce from 0 to 1400 eV

The soft-x-ray appearance potential spectra were measured for La and Ce in the 0-1400-eV range. The 3d and 4dspectra exhibited prominent structure, which is discussed along with x-ray absorption and emission data. The excited electron and the core hole interact strongly, and there is evidence for additional interaction with the projectile electron. The two-density-of-states model of Wendin seems promising for explaining the spectra, but it must be extended to allow for the interaction of the projectile electron with the excited atom. The effects of oxidation are described

Optical properties of crystalline tungsten

The optical properties of W are presented between 0.15 and 33 eV. The optical absorptivity or reflectivity was measured at near-normal incidence, and the data were Kramers-Kronig analyzed to determine the dielectric functions. Drude parameters were determined at low energy and were used to separate interband and intraband contributions to ε2. Structures in ε2 were apparent at 0.42, 0.97, 1.82, 2.35, 3.42, 5.25, 8.8, 11.3, 16.5, 22.5, and 31.5 eV. These features were discussed in terms of recent calculations of Christensen and Feuerbacher and by analogy to other transtion metals studied. The loss functions were shown to have three volume plasmons (25.3, 15.2, and 10.0 eV) and three surface plasmons (20.8, 14.8, and 9.7 eV). Structure near 31.5 eV was interpreted as due to NVII core transitions

Deformation Potentials for Excitons in Cuprous Halides

The hydrostatic-pressure shifts of the Z1,2 and Z3 exciton peaks were measured in thin films of cubic CuCl, CuBr, and CuI at 90 K. That of the E1 peak in CuI also was measured. The deformation potentials of all Z excitons and of the E1exciton in CuI, about -1 eV, are more than twice those of the Z excitons in CuCl and CuBr. This suggests the two valence bands in CuI may be considerably more mixed than in CuCl and CuBr

Optical properties of β′-CoAl

The optical absorptance of β′-CoAl in the (0.1-2.5)-eV region was measured and analyzed by the Kramers-Kronig method. The optical conductivity shows interband features beginning below 0.1 eV, with several structures below 2 eV. These structures agree with those calculated from the energy bands of Moruzzi, Williams, and Gelatt. The experimentally observed systematics in CoAl and NiAl confirm our previous interpretation of the spectra of β′-NiAl, and disagree with other experimental and theoretical attempts to understand the optical properties of these compounds

Optical properties of V, Ta, and Mo from 0.1 to 35 eV

The absorptivity or reflectivity of crystals of V, Ta, and Mo was measured from 0.1 to 35 eV. The data were Kramers-Kronig analyzed to determine the dielectric functions. The inadequacy of a simple Drude model to describe absorption at low energy is discussed. Structure in the dielectric functions is discussed in terms of direct interband transitions which extend to about 18 eV. Features below 6 eV are attributed to transitions near Σ, G, and perhaps along P(D)N for V, Ta, and Mo, with additional transitions in Mo from the Δ portion of the Brillouin zone. High-lying energy bands are identified as giving rise to high-energy structure in the dielectric functions. Results obtained previously for Nb are reviewed and compared. The electron-energy-loss functions were calculated and are discussed in terms of volume and surface plasmons. These metals all exhibit two volume and two surface plasmons