Resistivity and paraconductivity in the high-temperature superconductor yttrium barium(2) copper(3) oxygen(7-y)
Friedmann, Thomas Aquinas
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https://hdl.handle.net/2142/19161
Description
Title
Resistivity and paraconductivity in the high-temperature superconductor yttrium barium(2) copper(3) oxygen(7-y)
Author(s)
Friedmann, Thomas Aquinas
Issue Date
1991
Doctoral Committee Chair(s)
Ginsberg, Donald M.
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
We have measured the normal state resistivity of well characterized polycrystalline, twinned-single crystal, and twin-free single crystal samples of superconducting YBa$\sb2$Cu$\sb3$O$\sb{\rm 7-y}$. The resistivity was linear in temperature for all samples far from T$\sb{\rm c}$.
In polycrystalline samples the deviation from linearity near T$\sb{\rm c}$ has been analyzed in terms of the Aslamazov-Larkin three-dimensional (AL3D) fluctuation model on six separate samples. The value of the BCS superconducting-coherence length in the clean limit, $\xi\sb0$(0) = 13.4 $\pm$ 4.2A, has been extracted from the analysis. The Ginzburg criterion have been used to estimate H$\sb{\rm c2}$ $\cong$ 500 kG.
We have measured the ab plane resistivity of a twinned-single crystal of YBa$\sb2$Cu$\sb3$O$\sb{\rm 7-y}$. The data were fit to the Maki-Thompson, Aslamazov-Larkin, and Lawrence-Doniach (LD) models. All three theories could be fit to the data, but the LD theory gave the best fit, with physically reasonable parameters. We find that the Ginzburg-Landau coherence length in the c direction, extrapolated to low temperature, is approximately 0.44 A.
The resistivity tensor $\rho\sb{\rm a}$, $\rho\sb{\rm b}$, and $\rho\sb{\rm c}$, has been measured on two twin-free single crystal samples using a modified Montgomery technique. The room-temperature values of $\rho\sb{\rm a}$ and $\rho\sb{\rm b}$ are as small as any reported in the literature, which indicates good sample quality. The anisotropy ratio $\rho\sb{\rm a}$/$\rho\sb{\rm b}$, has been determined for the first time. Between 150K and 275K, the anisotropy ratio is temperature independent, and is equal to 2.2 $\pm$ 0.2. This results is in good agreement with recent infrared conductivity data measured by Schlesinger et al., and is also indicative of highly ordered chains. The $\rho\sb{\rm b}$ data show very little deviation from linearity near T$\sb{\rm c}$. The small rounding proves to be consistent with simple fluctuation theories; and it is possible to fit the a and b directions consistently to the LD and AL two-dimensional fluctuation models.
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