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Title:Resistivity and paraconductivity in the high temperature superconductor YBa2̳Cu3̳O7̳-̳y̳
Doctoral Committee Chair(s):Ginsberg, D.M.
Department / Program:Physics
single crystal
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.
Issue Date:1991
Genre:Dissertation / Thesis
Rights Information:1991 Thomas Aquinas Friedmann
Date Available in IDEALS:2011-05-10
Identifier in Online Catalog:3476424

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