Resistivity and paraconductivity in the high temperature superconductor YBa2̳Cu3̳O7̳-̳y̳
Submitter: Carolyn Mead
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https://hdl.handle.net/2142/23863
Description
Title
Resistivity and paraconductivity in the high temperature superconductor YBa2̳Cu3̳O7̳-̳y̳
Issue Date
1991
Doctoral Committee Chair(s)
Ginsberg, D.M.
Department of Study
Physics
Discipline
Physics
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
resistivity
paraconductivity
superconductor
polycrystalline
single crystal
Language
en
Abstract
We have measured the normal state resistivity of well
characterized polycrystalline, twinned-single crystal, and twinfree
single crystal samples of superconducting YBa2cu
3o7
_y· The
resistivity was linear in temperature for all samples far from T .
c
In polycrystalline samples the deviation from linearity near
Tc has been analyzed in terms of the Aslamazov-Larkin threedimensional
{AL3D) fluctuation model on six separate samples. The
value of the BCS superconducting-coherence length in the clean
limit, ~ 0 {0) = 13.4 ± 4.2A, has been extracted from the analysis.
The Ginzburg criterion have been used to estimate Hc
2 ~ 500 kG.
We have measured the ab plane resistivity of a twinnedsingle
crystal of YBa2cu3o7_y· The data were fit to the MakiThompson,
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, Pa' pb' and pc' has been measured on
two twin-free single crystal samples using a modified Montgomery
technique. The room-temperature values of Pa and pb are as small
as any reported in the literature, which indicates good sample
quality. The anisotropy ratio Pa/Pb' has been determined for the
first time. Between 150K and 275K, the anisotropy ratio is
temperature independent, and is equal to 2.2 ± 0.2. This result
is in good agreement with recent infrared conductivity data
measured by Schlesinger et al., and is also indicative of highly
ordered chains. The pb data show very little deviation from
linearity near Tc. 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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