Effect of Oxygen-Deficiency of CuO2 Plane on the Structure, Magnetism, and Transport Properties

Polycrystalline samples La_{2 – x} Sr _x CuO_{4 –} (0.06 x 1.0) and the corresponding vacuum annealed samples were investigated systematically by means of XRD, infrared (IR) spectra, ESR, and resistivity. It is found that the doping of Sr and the oxygen vacancies in CuO₂ planes show different effects on the lattice parameters a and c, and the changes of a and c of La_{2 – x} Sr _x CuO_{4 –} samples (x 0.2) rest with the cooperation of the two factors. The two high frequency IR vibration modes at 500 and 689 cm^–1, which are referred to the vibrations of apical oxygen and planar oxygen, are analyzed in detail. The disappearance of the mode at 689 cm^–1 is interpreted in terms of the screened effect of charge carriers in CuO₂ planes. ESR results indicate that oxygen deficiency of CuO₂ layers not only decreases carrier concentration, but also destroys the antiferromagnetic spin correlation or spin fluctuation and results in localized Cu²⁺ spins. The effect of localized Cu²⁺ spins (or spin scattering) on the superconductivity and transport properties is discussed in the text.     

Magnetic and Electrical Properties of Single-Crystal La1.99Sr0.01Cu1 ? yNiyO4

We report the out-of-plane and in-plane magnetic susceptibility and resistivity of Ni-doped La_1.99Sr_0.01CuO₄ single crystals grown by Traveling-Solvent Floating-Zone technique. Our data shows that in lightly Sr-doped compounds the Néel temperature T _N increased with increasing Ni concentration. At high temperatures, the resistivity is described within the impurity band conduction model. As the temperature is lowered, the resistivity behavior change to the variable range hopping model associated with the evolving of antiferromagnetic ordering.     

Evidence for strong electron-phonon interaction in point contact spectroscopy of superconducting oriented La1?xSrxCuO4

Point contact spectroscopy results obtained along the CuO planes an oriented LaSrCuO samples are presented. Both Andreev and tunneling contacts have been studied, up to 100 meV. The results are interpreted within the framework of a recent theory of inelastic transport through normal metal-superconductor interfaces, and both types of contacts are consistent with this theory. They point clearly to the electron-phonon interaction as the source of this inelastic scattering and of superconductivity in this cuprate.