Nuclear magnetic resonance studies of yttrium barium copper oxide in the superconducting state

Barrett, Sean Eric

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https://hdl.handle.net/2142/22911 Copy

Description

Title

Nuclear magnetic resonance studies of yttrium barium copper oxide in the superconducting state

Author(s)

Barrett, Sean Eric

Issue Date

1992

Doctoral Committee Chair(s)

Slichter, C.P.

Department of Study

Physics

Discipline

Physics

Degree Granting Institution

University of Illinois at Urbana-Champaign

Degree Name

Ph.D.

Degree Level

Dissertation

Keyword(s)

Physics, Condensed Matter

Language

eng

Abstract

• 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.

Type of Resource

text

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http://hdl.handle.net/2142/22911

Copyright and License Information

Copyright 1992 Barrett, Sean Eric

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