Abstract
The role of oxygen content parameter δ on the metal–insulator transition and superconductivity in oxygen-reduced Sm1.85Ce0.15CuO4+δ (−0.06<δ<0.08) antiferromagnetic superconductors (TN(Sm)∼4.6K) are reported. A superconductor–insulator transition was observed near δ∼0.05, with Tc (onset) of 11K for δ∼0.045, 18K for δ∼0.04, 20K for δ∼0.03 and maximum Tc up to 24K for δ∼−0.02. The relative oxygen content δ was determined using the Sm2CuO4 as the standard and based on Ce4+ from Ce LIII-edge X-ray absorption spectra. For tetragonal c-axis aligned Sm1.85Ce0.15CuO3.98 powder (Tc=24K), a non-s-wave or dirty d-wave-like T2 power law was observed for T<0.5Tc from in-plane penetration depth Δλab(T)=λab(T)−λab(0) data.
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