Atomic order, electron structure, and critical parameters of epitaxial YBaCuO films

Abstract

X-ray structural and optical methods were applied to make a detailed investigation of atomic and electronic structure of superconducting YBa2Cu3O7−δ films obtained by pulsed laser deposition. Optical transmission spectrum was found to depend not only on intraband (ℏω<1.2 eV) and interband (ℏω>1.95 eV) transitions, but also on contributions from charge transfer transitions O 2p⇒Cu 3d in the dielectric phase due to local order in a system of crystallographic (11l) planes. Superconducting properties of the films are determined by orientational structural transition (00l)+(11l)⇒(00l) and by Anderson type transition from a charge transfer O 2p⇒Cu 3d insulator to a strongly degenerate semiconductor with metallic conductivity. We show the effects of ordering on transition temperature Tc and demonstrate that at the concentration of (00l) clusters below the percolation threshold (20%) the behavior of Tc has catastrophic character.