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Salamon, Myron B. Inderhees, Sue Ellen 2011-05-07T13:38:41Z 2011-05-07T13:38:41Z 10000-01-01 1990 "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. Made available in DSpace on 2011-05-07T13:38:41Z (GMT). No. of bitstreams: 2 license.txt: 4922 bytes, checksum: 910b249b4beec47e7ab768910c8f966f (MD5) 9114278.pdf: 4733854 bytes, checksum: 0ba701f834da66673b0c5e7a50398c19 (MD5) Previous issue date: 1990 Item marked as restricted to the 'UIUC Users [automated]' Group (id=2) by Howard Ding (hding2@illinois.edu) on 2011-05-07T14:57:22Z Item is restricted indefinitely. Restriction data tranferred 2014-07-01T11:26:54-05:00 Original Data Group with Access UIUC Users [automated] Release Date: none Reason: ETDs are only available to UIUC Users without author permission ETDs are only available to UIUC Users without author permission U of I Only AAI9114278 (UMI)AAI9114278 http://hdl.handle.net/2142/22402 eng Copyright 1990 Inderhees, Sue Ellen Physics, Condensed Matter Heat capacity measurements of yttrium barium(2)copper(3)oxygen(7-delta) near T(c): Fluctuation effects in a bulk superconductor text Physics Physics University of Illinois at Urbana-Champaign Dissertation Ph.D.