Optical and magneto-optical properties and electronic structures of single-crystalline RAI(2) (R = Y, La, Ce, Pr, and Lu) - art. no. 035105

摘要

The diagonal optical conductivity spectra of single crystals of RAl2 (R=Y, La, Ce, Pr, and Lu) were measured at room temperature by spectroscopic ellipsometry in the 1.5-5.6-eV range. Ail the compounds exhibit two strong interband absorption peaks at about 1.8 and 3.6 eV for YAl2 and LuAl2, and at about 2.0 and 3.0 eV for LaAl2, CeAl2, and PrAl2. Such differences in the second peak position appear in the theoretical optical conductivity spectra calculated from their band structures obtained by the tight-binding linear-muffin-tin-orbitals method. Most of the contributions to the two peaks in LaAl2 are from the p and d states, i.e., p -->d and d-->p transitions, while those involving f states are negligible. These results suggest that f character near E-F for LaAl2, CeAl2, and PrAl2 distorts their conduction bands significantly through hybridization, leading to different optical spectra compared to those of YAl2 and LuAl2. The magneto-optical properties of CeAl2 and PrAl2 were measured at low temperatures. The Kerr rotation (Theta (K)) and ellipticity (epsilon (K)) for both compounds show similar spectral variations with maximum Theta (K) of 0.35 degrees and 0.55 degrees at about 2.1 eV for CeAl2 and PrAl2, respectively. The evaluated off-diagonal conductivity spectra of the two compounds are also similar, with two structures at about 2.1 and 3.8 eV for CeAl2 and 2.1 and 3.4 eV for PrAl2. The energy difference in the second structures is interpreted as due to the different conduction-band structures of the two compounds caused by different hybridization strengths of their f states with conduction bands, because of the difference in their degree of localization. [References: 37]