NMR Studies of ¹⁷O in the Normal State of YBa₂Cu₃O_6+x

Abstract

The temperature dependence of both the Knight shift (K) tensor and the nuclear spin-lattice relaxation rate (1⁄T₁) in the normal state have been studied, by using the magnetically oriented powered samples of YBa₂Cu₃O_6+x with x=0.96, 0.8 and 0.6. From the K−χ plot for the planer oxygen sites (O(2, 3)), we have determined the principal values of the hyperfine field tensor and found that those hardly depend on the hole concentration. The remarkable feature has emerged from the T-dependence of the 1⁄(T₁T) at the O(2, 3) sites; i.e. it reveals almost the same T-dependence of the spin parts of the Knight shift. This observation suggests that the energy width of the spin excitations around q∼0 is T-independent in the normal state. The Knight shift tensor at the apical oxygen sites has also been measured and is discussed.