Near-band gap electronic structure of the tetragonal rare-earth cuprates R 2 CuO 4 and the bismuth cuprate Bi 2 CuO 4

摘要: Complex optical dielectric function in the tetragonal rare-earth cuprates ${R}_{2}{\text{CuO}}_{4}$ ($R=\text{La}$, Pr, Nd, and Sm) bismuth cuprate ${\text{Bi}}_{2}{\text{CuO}}_{4}$ is studied spectral range of 0.6--5.4 eV using a method ellipsometry. The spectra are for two main polarizations analyzed terms cluster model ${\text{CuO}}_{4}^{6\ensuremath{-}}$ complexes taking into account intracenter $p\text{\ensuremath{-}}d$ intercenter $d\text{\ensuremath{-}}d$ charge-transfer (CT) transitions. band gap defined by an electric-dipole-allowed CT transitions centered at 1.54--1.59 Sm cuprates, 2.1 La cuprate. Optical response strongly differs from which we relate with strong covalency Bi-O bonding ionicity $\text{Cu}(3d)\text{-O}(2p)$ bonding. These features manifested suppression low-energy intense transitions, appearance absorption bands near 5 eV. Regardless distinctions response, on one hand, La, other Bi cuprate, these compounds shows comparable values superposition two-center Thus should be classified as intermediate between Mott-Hubbard insulators.