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Ginsberg, D.M. 2011-05-10T15:23:48Z 2011-05-10T15:23:48Z 10000-01-01 1991 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. Submitted by Carolyn Mead (cmead2@illinois.edu) on 2011-05-10T15:23:48Z No. of bitstreams: 1 1991_friedmann.pdf: 14076179 bytes, checksum: f5d16c928c3382a0af7906f691dbb18b (MD5) Made available in DSpace on 2011-05-10T15:23:48Z (GMT). No. of bitstreams: 1 1991_friedmann.pdf: 14076179 bytes, checksum: f5d16c928c3382a0af7906f691dbb18b (MD5) Previous issue date: 1991 Restriction data tranferred 2014-07-01T11:13:07-05:00 Original Data Group with Access UIUC Users [automated] Release Date: none Reason: Thesis Item marked as restricted to the 'UIUC Users [automated]' Group (id=2) by Carolyn Mead (cmead2@illinois.edu) on 2011-05-10T15:23:48Z Item is restricted indefinitely. Thesis U of I Only 3476424 http://hdl.handle.net/2142/23863 en 1991 Thomas Aquinas Friedmann resistivity paraconductivity superconductor polycrystalline single crystal Resistivity and paraconductivity in the high temperature superconductor YBa2̳Cu3̳O7̳-̳y̳ Dissertation / Thesis text Physics Physics University of Illinois at Urbana-Champaign Dissertation Ph.D.