Anisotropy and Phonon Modes from Analysis of the Dielectric Function Tensor and the Inverse Dielectric Function Tensor of Monoclinic Yttrium Orthosilicate

Authors

Alyssa Mock, University of Nebraska-LincolnFollow
Rafal Korlacki, University of Nebraska-LincolnFollow
Sean Knight, University of Nebraska-LincolnFollow
Mathias Schubert, University of Nebraska-LincolnFollow

Document Type

Article

Date of this Version

2018

Citation

Physical Review B 97, 165203 (2018)

DOI: 10.1103/PhysRevB.97.165203

Comments

Copyright 2018 by the American Physical Society

https://doi.org/10.1103/PhysRevB.97.165203

Abstract

We determine the frequency dependence of the four independent Cartesian tensor elements of the dielectric function for monoclinic symmetry Y₂SiO₅ using generalized spectroscopic ellipsometry from 40–1200 cm⁻¹. Three different crystal cuts, each perpendicular to a principle axis, are investigated. We apply our recently described augmentation of lattice anharmonicity onto the eigendielectric displacement vector summation approach [A.Mock et al., Phys. Rev. B 95, 165202 (2017)], and we present and demonstrate the application of an eigendielectric displacement loss vector summation approach with anharmonic broadening. We obtain an excellent match between all measured and model-calculated dielectric function tensor elements and all dielectric loss function tensor elements. We obtain 23 A_u and 22 B_u symmetry long-wavelength active transverse and longitudinal optical mode parameters including their eigenvector orientation within the monoclinic lattice. We perform density functional theory calculations and obtain 23 A_u symmetry and 22 B_u transverse and longitudinal optical mode parameters and their orientation within the monoclinic lattice. We compare our results from ellipsometry and density functional theory and find excellent agreement. We also determine the static and above reststrahlen spectral range dielectric tensor values and find a recently derived generalization of the Lyddane-Sachs-Teller relation for polar phonons in monoclinic symmetry materials satisfied [M. Schubert, Phys Rev. Lett. 117, 215502 (2016)].