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Temperature-dependent far-infrared reflectance of La-Sr-Cu-O and La-Ca-Cu-O: Bardeen-Cooper-Schrieffer electrodynamics but uncertain energy gap

Journal Article · · Phys. Rev. B: Condens. Matter; (United States)
; ;
The available far-infrared data for polycrystalline La-Sr-Cu-O and La-Ca-Cu-O show a reflectance edge with energy near 2.5k/sub B/T/sub c/. This edge has been variously interpreted as the onset of absorption due to an energy gap, and as a low-frequency plasma edge caused by strong far-infrared resonances. Our measured temperature dependence of the reflectance edge closely fits the temperature dependence of the order parameter in a mean-field theory, and hence is consistent with the energy-gap hypothesis. In this paper, we construct a model dielectric function for La/sub 1.85/Sr/sub 0.15/CuO/sub 4/ which is consistent with mean-field theory and the hypothesis of a plasma edge. We find that the temperature dependence of the plasma frequency in this model also closely fits the measured temperature dependence of the reflectance edge. Furthermore, both hypotheses accurately predict the experimentally observed temperature dependence of the absorption at frequencies much less than the reflectance edge. This observation has significant implications for the construction of fast low-loss superconducting devices. We conclude that the electrodynamics of the superconducting transition in La/sub 1.85/Sr/sub 0.15/CuO/sub 4/ are well described by a Bardeen-Cooper-Schrieffer-like mean-field theory. However, given the identical predictions of the energy-gap and plasma-edge hypotheses, it is premature to deduce a precise value for the magnitude of the energy gap from the infrared data.
Research Organization:
Department of Physics, University of California, Berkeley, California 94720
OSTI ID:
5619803
Journal Information:
Phys. Rev. B: Condens. Matter; (United States), Journal Name: Phys. Rev. B: Condens. Matter; (United States) Vol. 37:4; ISSN PRBMD
Country of Publication:
United States
Language:
English

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Related Subjects

36 MATERIALS SCIENCE
360204* -- Ceramics
Cermets
& Refractories-- Physical Properties
656100 -- Condensed Matter Physics-- Superconductivity
75 CONDENSED MATTER PHYSICS
SUPERCONDUCTIVITY AND SUPERFLUIDITY
ALKALINE EARTH METAL COMPOUNDS
BCS THEORY
CALCIUM COMPOUNDS
CALCIUM OXIDES
CHALCOGENIDES
COPPER COMPOUNDS
COPPER OXIDES
CRYSTALS
ELECTROMAGNETIC RADIATION
ENERGY GAP
FAR INFRARED RADIATION
INFRARED RADIATION
LANTHANUM COMPOUNDS
LANTHANUM OXIDES
MEAN-FIELD THEORY
OPTICAL PROPERTIES
OXIDES
OXYGEN COMPOUNDS
PHYSICAL PROPERTIES
POLYCRYSTALS
RADIATIONS
RARE EARTH COMPOUNDS
REFLECTIVITY
STRONTIUM COMPOUNDS
STRONTIUM OXIDES
SUPERCONDUCTORS
SURFACE PROPERTIES
TEMPERATURE DEPENDENCE
TRANSITION ELEMENT COMPOUNDS