Physical Review B (Impact Factor: 3.74). 11/2011; 84(19). DOI: 10.1103/PhysRevB.84.195439
Generalized ellipsometry measurements were made using 12 orientations of a monoclinic CdWO4 crystal. Using these measurements and the associated analytical methods presented here, it is shown that the four independent complex elements of the dielectric tensor can be determined at each wavelength. Below the band edge (similar to 4 eV), the dielectric tensor is real, and, therefore, it is possible to uniquely diagonalize the dielectric tensor and determine the birefringence for light passing along the unique axis, but the orientation of the dielectric tensor axes will be a function of wavelength. Above the band edge, unique diagonalization is not possible. The generalized ellipsometric spectra show some symmetry in the cross-polarization coefficients. When the unique axis is perpendicular to the sample surface, the condition rho(ps) = -rho(sp) is valid. If the unique axis is perpendicular to the plane of incidence, rho(sp) = rho(ps) = 0, and if the unique axis is in the plane of incidence, parallel to the sample surface, then rho(ps) = rho(sp) not equal 0. The combined experimental and analytical methods described here are applicable to the determination of the spectroscopic dielectric tensors of monoclinic crystals in general.
[Show abstract][Hide abstract] ABSTRACT: A method is introduced to correlate electromagnetic theory and polarimetric experiments for anisotropic optically active crystals at oblique angles of incidence. It is based on the 4 × 4 algebraic descriptions of light propagation in layered anisotropic media, which can be simplified to 2 × 2 matrices when multiple reflections are disregarded. Spectroscopic Mueller matrix measurements in transmission and at oblique angles of incidence have been made on two uniaxial crystals: α‐quartz and silver thiogallate. Their optical activity tensors have been spectroscopically determined using the method presented here.
[Show abstract][Hide abstract] ABSTRACT: The four real values of the dielectric function tensor of the monoclinic crystal Lu2SiO5 or lutetium oxyorthosilicate (LSO) have been determined using generalized ellipsometry from 200 to 850 nm. The three principal values are fit to the Sellmeier model, and they indicate that the band gap of LSO is less than ~9 eV. The off-diagonal element 12 is non-zero over the entire spectrum, but it is very close to zero for wavelengths longer than ~400 nm, indicating that structurally monoclinic LSO is nearly optically orthorhombic in this wavelength region. The spectroscopic dielectric functions of three isotropic ceramic LSO samples are presented, which are consistent with the dielectric functions of single-crystal LSO when the effects of porosity are included. As a comparison, the dielectric functions are also determined using relativistic electronic structure and optical calculations based on the recently developed potential functional of Tran and Blaha (Phys. Rev. Lett. 102, 226401 (2009).)
[Show abstract][Hide abstract] ABSTRACT: The full quasiparticle band structure of CdWO4 is calculated within the single-shot GW (G0W0) approximation using maximally localized Wannier functions, which allows one to assess the validity of the commonly used scissor operator. Calculations are performed using the Godby-Needs plasmon pole model and the accurate contour deformation technique. It is shown that while the two methods yield identical band gap energies, the low-lying states are given inaccurately by the plasmon pole model. We report a band gap energy of 4.94 eV, including spin-orbit interaction at the DFT-LDA (density functional theory-local density approximation) level. Quasiparticle renormalization in CdWO4 is shown to be correlated with localization distance. Electron and hole effective masses are calculated at the DFT and G0W0 levels.
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