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Slichter, C.P. Barrett, Sean Eric 2011-05-03T16:58:57Z 2011-05-03T16:58:57Z 1992 In this thesis we report measurements of the 63Cu Knight shift in the · superconducting state for the plane (Cu(2)) and Chain (Cu(l)) sites in YBa2Cu307. We also have measured the temperature and field dependent 63Cu(2) nuclear spin relaxation rates (63Wla) in the superconducting state. The accurate determination of the 63Cu Knight shift below Tc required a precise knowledge of the magnetic field strength inside the bulk of the sample. We have used 89y as an internal field marker to determine the amount of diamagnetic shielding present in our sample below T c· Observation of the 89y resonance in the superconducting state required several unusual NMR techniques, such as using the Carr-Purcell-MeiboomGill 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 temperature dependence of the Cu(l) Knight shift is slightly different from the temperature dependence of the Cu(2) Knight shift. It is possible to fit the data assuming either an orbitals-wave or an orbital d-wave pairing state, but in every case the energy gap seen by the Cu(2) apparently possesses a strong coupling temperature dependence, while the energy gap seen by the Cu(l) is much closer to the weak coupling gap assumed in the original BCS theory. During our measurements of the temperature dependence of the Cu(2) spin-lattice relaxation rates in the superconducting state (63W1 a.; where ~ . 1\ HoI 1-a.), we discovered that the anisotropy ratio 63W1aj63W1c, which was essentially independent of temperature in the normal state, drops sharply just below Tc (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- 77 K the anisotropy ratio 63W1a/63W1c 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 dwave pairing state, but are unable to fit our data assuming a spin-singlet, orbital s-wave pairing state. We also observe a sizeable field dependence of the spin-lattice relaxation rate in the superconducting state, which is much more pronounced when the magnetic field penetrates the Cu02 planes (63W1c) than when the field lies along the Cu02 planes (63W1a). These rates appear to be linearly dependent upon the field, indicating that flux lines may be contributing to the observed relaxation rates. Submitted by Carolyn Mead (cmead2@illinois.edu) on 2011-05-03T16:58:57Z No. of bitstreams: 1 1992_barrett.pdf: 6605253 bytes, checksum: 7e15090e9604604f817e13101660a938 (MD5) Made available in DSpace on 2011-05-03T16:58:57Z (GMT). No. of bitstreams: 1 1992_barrett.pdf: 6605253 bytes, checksum: 7e15090e9604604f817e13101660a938 (MD5) Previous issue date: 1992 Restriction data tranferred 2014-07-01T11:12:16-05:00 Original Data Group with Access UIUC Users [automated] Release Date: none Reason: Thesis Item marked as restricted to the 'UIUC Users [automated]' Group (id=2) by Carolyn Mead (cmead2@illinois.edu) on 2011-05-03T16:58:57Z Item is restricted indefinitely. Open Restriction set for Item 19034 on 2020-11-10T17:54:30Z with date null by bran3@illinois.edu. Open Restriction set by bran3 at author's request. Open Restriction set for Item 19034 on 2020-11-10T17:56:57Z with date null by bran3@illinois.edu. Open Restriction set for Item 19034 on 2020-11-10T17:59:24Z with date null by bran3@illinois.edu. Open 3478448 http://hdl.handle.net/2142/18902 en 1992 Sean Eric Barrett nuclear magnetic resonance superconducting Knight shift copper nuclear spin relaxation rates superconducting state Nuclear magnetic resonance studies of YBa2̳Cu3̳07̳ in the superconducting state Dissertation / Thesis text Physics Physics University of Illinois at Urbana-Champaign Dissertation Ph.D.