Barium nuclear magnetic resonance spectroscopic study of YBa2Cu3O7

We have measured the Ba135 nuclear magnetic resonance (NMR) line shape and the Ba137 nuclear quadrupole resonance (NQR) of a powder sample of YBa2Cu3O7, at 300 K, as well as the temperature and field dependences of the Ba135,137 NMR line shapes and spin-lattice relaxation rates of magnetically aligned (c?H0) samples, in the normal and superconducting states. From the NQR and the field and isotopic dependences of the NMR line shapes of magnetically aligned samples at 300 K, we conclude that the magnetic shift is small (0.00.12%), and that the principal components of the electric-field gradient tensor are (8.3,-0.2,-8.1)×1021 V m-2, with the largest component coincident with the crystallographic c axis. In the superconducting state, the resonances broaden and are shifted to lower frequency. The spin-lattice relaxation behavior is not Korringa-like above Tc, and may be influenced by spin fluctuations in the CuO2 plane.