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Title:A low temperature calorimetric study of several high-T(c) superconductors
Author(s):Reeves, Mark Edwin
Doctoral Committee Chair(s):Ginsberg, Donald M.
Department / Program:Physics
Degree Granting Institution:University of Illinois at Urbana-Champaign
Subject(s):Physics, Condensed Matter
Abstract:Sintered powders of La$\sb{1.85}$Ba$\sb{0.15}$CuO$\sb4$, La$\sb{1.8}$Sr$\sb{0.2}$CuO$\sb4$, YBa$\sb2$Cu$\sb3$O$\sb{\rm7-x}$, and GdBa$\sb2$Cu$\sb3$O$\sb{\rm 7-x}$ were prepared by solid state reaction. The samples were carefully characterized for impurities by x-ray diffraction and Raman spectroscopy. The resistivity and magnetic susceptibility of each sample was measured to characterize its superconducting transition.
The specific heat of the samples was measured with an adiabatic, computer-controller calorimeter. The specific heat discontinuity for GdBa$\sb2$Cu$\sb3$O$\sb{\rm 7-x}$ was determined, and antiferromagnetic ordering and superconductivity were observed to coexist in this sample. For all the samples, a temperature dependent phonon density of states was inferred from the specific heat measured above 10K.
While the temperature range of the measurements extended from 2 to 180K, particular attention was paid to the specific heat below 10K. In this temperature range, the lattice and electronic contributions to the specific heat could be separated. In all the samples measured except for GdBa$\sb2$Cu$\sb3$O$\sb{\rm 7-x}$ an unexpected linear contribution to the specific heat was observed. By systematically eliminating the known impurities in a sample of YBa$\sb2$Cu$\sb3$O$\sb{\rm 7-x}$ and still observing the linear contribution, we argue against attributing this contribution to a parasitic phase.
The magnetic field dependence of the specific heat of YBa$\sb2$Cu$\sb3$O$\sb{\rm 7-x}$ was determined for fields from 0 to 3T and in the temperature range 2 to 10K. The field dependence was compared to a calculation based on Ginzburg-Landau theory. The theory did not predict our experimental results.
Issue Date:1989
Rights Information:Copyright 1989 Reeves, Mark Edwin
Date Available in IDEALS:2011-05-07
Identifier in Online Catalog:AAI9010996
OCLC Identifier:(UMI)AAI9010996

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