## Files in this item

FilesDescriptionFormat

application/pdf

9114278.pdf (5MB)
(no description provided)PDF

## Description

 Title: Heat capacity measurements of yttrium barium(2)copper(3)oxygen(7-delta) near T(c): Fluctuation effects in a bulk superconductor Author(s): Inderhees, Sue Ellen Doctoral Committee Chair(s): Salamon, Myron B. Department / Program: Physics Discipline: Physics Degree Granting Institution: University of Illinois at Urbana-Champaign Degree: Ph.D. Genre: Dissertation Subject(s): Physics, Condensed Matter Abstract: High-resolution ac heat capacity measurements of YBa$\sb2$Cu$\sb3$O$\sb{\rm 7-\delta}$ near the critical temperature are reported and discussed. The samples are high-quality single crystals, several of which display untwinned regions making up at least 50% of the sample mass. The heat capacity data show a cusp-like anomaly instead of the discontinuous step observed in "classic" superconductors. This divergence is indicative of the presence of fluctuation contributions and is due to the exceptionally short Ginzburg-Landau coherence length of this material. Because there is considerable uncertainty in the temperature of cross-over from mean-field to critical behavior, the zero-field heat capacity data are analyzed both as a lowest-order correction to mean-field BCS theory (the Gaussian approximation) and in terms of true critical behavior. The analysis shows that the data are best described within the Gaussian approximation as three-dimensional fluctuations of a two-component order parameter, but the results do not rule out a more complicated order parameter or a logarithmic (critical) divergence. The underlying BCS step indicates strong-coupling behavior.Application of a magnetic field broadens and suppresses the heat capacity transition, with no apparent shift in the onset of superconductivity, and with the effects more pronounced for fields applied parallel to the c-axis than for fields in the ab-plane. We find this behavior cannot be explained in terms mean-field theory. Rather, the anisotropic broadening and suppression may be understood in the context of critical finite-size scaling, since the length scale of the fluctuations is essentially restricted to values less than the lowest-order Landau radius in directions perpendicular to the applied field. Issue Date: 1990 Type: Text Language: English URI: http://hdl.handle.net/2142/22402 Rights Information: Copyright 1990 Inderhees, Sue Ellen Date Available in IDEALS: 2011-05-07 Identifier in Online Catalog: AAI9114278 OCLC Identifier: (UMI)AAI9114278
﻿