NMR of 17 O and 63 Cu in uniaxially aligned superconductor YBa 2 Cu 3 O 7-δ

Abstract

We have performed 17 O and 63 Cu NMR measurements in YBa 2 Cu 3 O 6.85 oriented powder samples at the CuO 2 plane sites Cu(2) and O(2,3) in the temperature range from 10 to 300 K. The temperature dependent Knight shift K and spin lattice relaxation rate T −1 1 of O(2,3) yield K 2 T 1 T = const in accordance with the presence of free carriers at the plane oxygen sites. A sharp decrease of T −1 1 of Cu(2) below T AF ≈ 1.5 T c is associated with the opening of a gap in the spectrum of antiferromagnetic spin fluctuations of localized copper 3d 9 electrons. Comparison of the different temperature dependences of spin densities at the Cu and O sites shows the presence of two nearly independent spin systems in close similarity with heavy fermion superconductors. A magnetic mechanism of high temperature superconductivity in doped CuO 2 layers is suggested.