Kondo effect and superconductivity in Nd2-xCexCuO4- delta compounds.

Abstract

Samples of ${\mathrm{Nd}}_{2\mathrm{\ensuremath{-}}\mathrm{x}}$${\mathrm{Ce}}_{\mathrm{x}}$${\mathrm{CuO}}_{4\mathrm{\ensuremath{-}}\mathrm{\ensuremath{\delta}}}$ (0\ensuremath{\le}x\ensuremath{\le}0.2) were prepared by annealing both in air and under vacuum (${10}^{\mathrm{\ensuremath{-}}5}$ Torr). Powder x-ray-diffraction patterns indicated that all samples consisted of a single-phase ${\mathrm{Nd}}_{2}$${\mathrm{CuO}}_{4}$-type tetragonal structure with crystal symmetry I4/mmm. Electrical resistivity measurements showed that all Ce-doped ${\mathrm{Nd}}_{2}$${\mathrm{CuO}}_{4\mathrm{\ensuremath{-}}\mathrm{\ensuremath{\delta}}}$ samples annealed in air and those annealed in vacuum with x<0.17 demonstrate a resistivity minimum (Kondo effect) resulting from the combination of magnetic and phonon scattering. Magnetic susceptibility and electrical resistivity measurements reflect the influence of crystal-field effects below 55 K. The linear temperature-dependent term of the resistivity typical of metallic behavior in the high-${T}_{c}$ oxides exists across the whole range of Ce concentration, with the exception of the host compound ${\mathrm{Nd}}_{2}$${\mathrm{CuO}}_{4\mathrm{\ensuremath{-}}\mathrm{\ensuremath{\delta}}}$, which is an insulator. This indicates that a model of metal-insulator transition is not appropriate in describing the occurrence of superconductivity in ${\mathrm{Nd}}_{2\mathrm{\ensuremath{-}}\mathrm{x}}$${\mathrm{Ce}}_{\mathrm{x}}$${\mathrm{CuO}}_{4\mathrm{\ensuremath{-}}\mathrm{\ensuremath{\delta}}}$.