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Slichter, C.P. Barrett, Sean Eric 2011-05-07T13:55:37Z 2011-05-07T13:55:37Z 1992 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 $\sp{89}$Y NMR as an internal field marker. The $\sp{89}$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 $\rm\vec Ho\vert~\vert\\alpha$), 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 $<$ T $<$ Tc). The data which we have measured in the smallest fields possible (Ho $<$ 4.5 kGauss) show that as the temperature is lowered below T $\sim$ 77 K the anisotropy ratio $\sp{63}$W1a/$\sp{63}$W1c starts to increase, eventually exceeding the normal state anisotropy ratio. These low field data have been interpreted by several groups in terms of a generalized BCS pairing state. These groups successfully fit our data assuming a spin-singlet, orbital d-wave pairing state, but are unable to fit our data assuming a spin-singlet, orbital s-wave pairing state. The application of magnetic field which penetrates the CuO$\sb2$ planes produces a sizeable linear dependence of the relaxation rate ($\sp{63}$W1c) upon the field below Tc. Made available in DSpace on 2011-05-07T13:55:37Z (GMT). No. of bitstreams: 2 license.txt: 4922 bytes, checksum: 910b249b4beec47e7ab768910c8f966f (MD5) 9215775.pdf: 7757215 bytes, checksum: 17f97df0b21114eedf26105615633dcf (MD5) Previous issue date: 1992 Item marked as restricted to the 'UIUC Users [automated]' Group (id=2) by Howard Ding (hding2@illinois.edu) on 2011-05-07T15:00:52Z Item is restricted indefinitely. Restriction data tranferred 2014-07-01T11:28:50-05:00 Original Data Group with Access UIUC Users [automated] Release Date: none Reason: ETDs are only available to UIUC Users without author permission Open Restriction set for Item 23046 on 2020-11-10T17:57:25Z with date null by bran3@illinois.edu. Open Restriction set by bran3 at author's request. Open Restriction set for Item 23046 on 2020-11-10T17:59:42Z with date null by bran3@illinois.edu. Open AAI9215775 (UMI)AAI9215775 http://hdl.handle.net/2142/22911 eng Copyright 1992 Barrett, Sean Eric Physics, Condensed Matter Nuclear magnetic resonance studies of yttrium barium copper oxide in the superconducting state text Physics Physics University of Illinois at Urbana-Champaign Dissertation Ph.D.