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Title:Nuclear resonance studies of the superconducting state of YBa2Cu3O7
Author(s):Martindale, Joseph Adam
Doctoral Committee Chair(s):Slichter, C.P.
Department / Program:Physics
Subject(s):nuclear spin-lattice relaxation rates
Abstract:The author reports measurements of nuclear spin-lattice relaxation rates w1 for the planar 63Cu(2) and 170(2,3) sites in YBa2Cu307 (T c=93K). We have observed a dependence of the rates in the superconducting state on the strength of the applied magnetic field H0 , with strong fields causing an increase in the measured rates. This effect was much greater for fields along the crystalline c axis than for fields applied in the a-b plane and is presumed to result from fluxoids since the relaxation rates were found to depend more or less linearly on the field strength. We therefore used weak magnetic fields in order to obtain the true superconducting-state behavior of the relaxation rates. Our measurements of the copper rates 63W 1 a (for Ho┴c) and 63W 1c (for Ho||2) in weak magnetic fields revealed an unexpected result for T < Tc: the ratio 63W 1 af63W 1 c which was essentially independent of temperature in the normal state, decreased upon entering the superconducting state with a minimum for T ,. 80 K but then increased as the temperature was decreased below 80 K. Also, our weak-field data for 63W 1 c and 17W 1 c showed that these rates varied approximately as T3 at low temperature, which is the expected temperature dependence for an orbital d-wave pairing state. In addition, unlike previous measurements, the ratio of copper-to-oxygen rates 63W 1 cf17W 1 c was found to be dependent on temperature in the superconducting state; the ratio was constant for 77 K < T < 100 K with a value of approximately 22 but decreased as the temperature decreased, to a value of 7.5 at 17 K. Several theoretical calculations employing a generalized BCS approach have been able to explain all of the NMR data from the superconducting state by assuming an orbital d-wave pairing state whereas an orbital s-wave pairing state with an isotropic gap failed to account for the data.
Issue Date:1993
Genre:Dissertation / Thesis
Rights Information:1993 Joseph Adam Martindale
Date Available in IDEALS:2012-01-20

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