UC Irvine

We present our 17O NMR experimental results in a magnetically aligned powder sample of YBa2Cu3O7-δ (Tc = 93 K). The sign of the anisotropic Knight shift shows that the spin density resides mainly on the pσ orbitals at the planar O(2,3) and bridging O(4) sites. About 30 % of the total spin susceptibility is attributed to the oxygen 2pσ states. The Knight shift at the O(2,3) sites decrease more rapidly than that at the chain O(1) sites, indicating a larger gap in the planes. The nuclear relaxation rate at the O(2,3) sites shows linear-T (Korriga) behavior above Tc, in contrast to the much weaker temperature dependence at the planar Cu(2) sites. However, these two rates show identical temperature dependence below about 110 K, indicating that an important change in the spin dynamics takes place above Tc. © 1989.