Heat-capacity measurements of YBa sub 2 Cu sub 3 O sub 7 minus. delta. near Tc : Fluctuation effects in a bulk superconductor
Thesis/Dissertation
·
OSTI ID:5462658
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, but the results do not rule out a more complicated order parameter or a logarithmic (critical) divergence. 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 that for fields in the ab-plane.
- Research Organization:
- Illinois Univ., Urbana, IL (United States)
- OSTI ID:
- 5462658
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
36 MATERIALS SCIENCE
360204* -- Ceramics
Cermets
& Refractories-- Physical Properties
ALKALINE EARTH METAL COMPOUNDS
BARIUM COMPOUNDS
BARIUM OXIDES
CHALCOGENIDES
COHERENCE LENGTH
COPPER COMPOUNDS
COPPER OXIDES
DIMENSIONS
FLUCTUATIONS
FUNCTIONS
GAUSS FUNCTION
GINZBURG-LANDAU THEORY
HIGH-TC SUPERCONDUCTORS
LENGTH
ORDER PARAMETERS
OXIDES
OXYGEN COMPOUNDS
PHYSICAL PROPERTIES
SPECIFIC HEAT
SUPERCONDUCTORS
THERMODYNAMIC PROPERTIES
TRANSITION ELEMENT COMPOUNDS
VARIATIONS
YTTRIUM COMPOUNDS
YTTRIUM OXIDES
360204* -- Ceramics
Cermets
& Refractories-- Physical Properties
ALKALINE EARTH METAL COMPOUNDS
BARIUM COMPOUNDS
BARIUM OXIDES
CHALCOGENIDES
COHERENCE LENGTH
COPPER COMPOUNDS
COPPER OXIDES
DIMENSIONS
FLUCTUATIONS
FUNCTIONS
GAUSS FUNCTION
GINZBURG-LANDAU THEORY
HIGH-TC SUPERCONDUCTORS
LENGTH
ORDER PARAMETERS
OXIDES
OXYGEN COMPOUNDS
PHYSICAL PROPERTIES
SPECIFIC HEAT
SUPERCONDUCTORS
THERMODYNAMIC PROPERTIES
TRANSITION ELEMENT COMPOUNDS
VARIATIONS
YTTRIUM COMPOUNDS
YTTRIUM OXIDES