Growth and anisotropic superconducting properties of Nd_2–xCe_xCu0_4–y single crystals

Abstract

ELECTRON-DOPED copper oxide superconductors have recently been discovered in the system Ln_2–xCe_xCuO_4–y, where Ln is Pr, Nd or Sin^1,2. Here we report the growth of single crystals of Nd_2–xCe_xCuO_4–y, and measurements of their anisotropic superconducting properties. A sharp superconducting transition is observed at 22.5 K in Nd_1.84Ce_0.16CuO_4–y. The resistivity shows a metallic temperature dependence both parallel and perpendicular to the basal plane. Applying a magnetic field perpendicular to the basal plane causes a parallel shift of the resistive transition curve to lower temperatures, as in conventional type II superconductors but unlike the hole-doped copper oxide superconductors. The Ginzburg–Landau coherence lengths estimated from the resistively defined upper critical magnetic field are 70.2 Å in the basal plane and 3.4 Å along the c axis, showing an anisotropy factor of 21. This value is much larger than that in La_2–xSr_xCuO_4–y despite their apparent structural similarities. Crystallographic differences from the hole-doped systems and the concomitant changes in electronic properties may offer clues to the role of the Cu–O planes in the microscopic pairing mechanism of high-temperature superconductors.