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

The diagonal optical conductivity spectra of single crystals of RAl2 (R=Y, La, Ce, Pr, and Lu) were measured at room temperature by spectroscopic elli psometry in the 1.5-5.6-eV range. Ail the compounds exhibit two strong inte rband absorption peaks at about 1.8 and 3.6 eV for YAl2 and LuAl2, and at a bout 2.0 and 3.0 eV for LaAl2, CeAl2, and PrAl2. Such differences in the se cond peak position appear in the theoretical optical conductivity spectra c alculated from their band structures obtained by the tight-binding linear-m uffin-tin-orbitals method. Most of the contributions to the two peaks in La Al2 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 chara cter near E-F for LaAl2, CeAl2, and PrAl2 distorts their conduction bands s ignificantly through hybridization, leading to different optical spectra co mpared 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 vari ations 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 conductiv ity spectra of the two compounds are also similar, with two structures at a bout 2.1 and 3.8 eV for CeAl2 and 2.1 and 3.4 eV for PrAl2. The energy diff erence in the second structures is interpreted as due to the different cond uction-band structures of the two compounds caused by different hybridizati on strengths of their f states with conduction bands, because of the differ ence in their degree of localization.