Nuclear Magnetic Resonance Studies of Yttrium Barium Copper Oxide in the Superconducting State

Résumé du livre

In this thesis we report measurements of the $sp{63}$Cu Knight shift in the superconducting state for the plane (Cu(2)) and chain (Cu(1)) sites in YBa$sb2$Cu$sb3$O$sb7$. We also have measured the temperature and field dependent $sp{63}$Cu(2) nuclear spin relaxation rates ($sp{63}$W1$alpha$) in the superconducting state. Our determination of the $sp{63}$Cu Knight shift below T$sb{rm c}$ compensated for the diamagnetic shielding of our sample by using $sp9$Y NMR as an internal field marker. The $sp9$Y resonance was observed in the superconducting state using the Carr-Purcell-Meiboom-Gill pulse sequence to enhance the signal-to-noise ratio. We have interpreted our Knight shift data within a generalized Bardeen-Cooper-Schrieffer (BCS) pairing theory, and find that a spin-singlet pairing state is strongly favored by these data. The data are consistent with either an orbital s-wave or an orbital d-wave pairing state. While we can fit the Cu(2) data with a strong coupling energy gap, the Cu(1) data require a weak coupling gap. During our measurements of the temperature dependence of the Cu(2) spin-lattice relaxation rates in the superconducting state ($sp{63}$W1$alpha$, where $rmvec Hovert~vert\alpha$), we discovered that the anisotropy ratio $sp{63}$W1a/$sp{63}$W1c, which was essentially independent of temperature in the normal state, drops sharply just below T$sb{rm c}$(77 K $