NMR and NQR Studies of17O and63Cu in CuO2Plane of High-TcYBa2Cu3O6.65withTc=61 K

Abstract

The microscopic property of each oxygen and copper site in the CuO ₂ plane of YBa ₂ Cu ₃ O _6.65 with T _c =61 K has been investigated by ¹⁷ O NMR and ⁶³ Cu NQR techniques. It has been found that the nuclear spin-lattice relaxation rate 1/ T ₁ for Cu sites is depressed by three orders of magnitude as compared with that for YBa ₂ Cu ₃ O ₇ with T _c =92 K, whereas 1/ T ₁ for oxygen sites exhibits a rather small change, decreasing approximately to one-fourth (1/4). From this difference of the relaxation behavior between oxygen and Cu sites, it is derived that the progressive reduction of 1/ T ₁ for oxygen sites is responsible for the decrease of the p -hole carriers, while the extraordinary decrease of 1/ T ₁ for Cu sites is due to the dramatic suppression of the low-frequency components of an antiferromagnetic spin fluctuation of nearly localized d electrons. The spin fluctuation at the Cu sites is found to strongly correlate with the p -hole content.