Metal-insulator transition in double cobaltites RBaCo2O5.5 (R = Eu, Gd): Specific features of their optical properties

• Published in: Physics of the solid state Vol. 51; no. 3; pp. 525 - 531
• Main Authors: Makhnev, A. A., Nomerovannaya, L. V., Strel’tsov, S. V., Anisimov, V. I., Barilo, S. N., Shiryaev, S. V.
• Format: Journal Article
• Language: English
• Published: Dordrecht SP MAIK Nauka/Interperiodica 01.03.2009
• Subjects: Optical Properties; Physics; Physics and Astronomy; Solid State Physics; 78.20.Ci; 71.30.+h; 75.47.Pq; 71.20.Eh
• ISSN: 1063-7834; 1090-6460
• DOI: 10.1134/S1063783409030159

The temperature dependence of the optical properties of GdBaCo 2 O 5.5 in the region of the metal-insulator transition was studied in the spectral range λ = 4.0–0.258 μm ( E = 0.3–4.8 eV) by the spectroscopic ellipsometry method. The electronic structure of the crystal at T = 300 K was calculated by the linearized muffin-tin orbital method in the local-density approximation with inclusion of on-site Coulomb interaction (LDA + U ). The general features of the behavior of the optical properties of GdBaCo 2 O 5.5 and EuBaCo 2 O 5.5 are discussed. It is shown that the optical response on the metal side of the metal-insulator transition is determined by the redistribution of the optical-conductivity spectral weight in going from high to low energies and is significantly incoherent in character. The optical band gap width of the GdBaCo 2 O 5.5 is experimentally determined to be E g = 0.26 eV, which is close to a theoretical estimate. The type of interband transitions is determined from analyzing the temperature dependence of the optical functions for absorption bands.