Far-infrared conductivity and anomalous below-gap absorption in superconducting granular NbN
The far-infrared (10--100 cm/sup -1/) complex conductivity of superconducting granular NbN films has been determined from reflection and transmission data. Moderately granular films, with R/sub D'Alembertian/ = 150 and 200 ..cap omega../D'Alembertian, followed Leplae-modified Bardeen-Cooper-Schrieffer-- theory predictions with no absorption below the gap frequency ..omega../sub g/. The derived values of 2..delta../kT/sub c/ were 3.8 and 4.0, slightly below the results for homogeneous films. Highly granular films, with R/sub D'Alembertian/> or =500 ..cap omega../D'Alembertian, displayed dc resistive tails and evidence of Josephson coupling. The real part of the far-infrared conductivity was BCS-type for frequencies above ..omega../sub g/ but showed an anomalous absorption below ..omega../sub g/. This excess absorption may arise from two-dimensional fluctuations in the form of vortices or from normal conducting regions mixed in with the superconducting grains.
- Research Organization:
- Physics Department, Emory University, Atlanta, Georgia 30322
- OSTI ID:
- 5771832
- Journal Information:
- Phys. Rev. B: Condens. Matter; (United States), Journal Name: Phys. Rev. B: Condens. Matter; (United States) Vol. 27:9; ISSN PRBMD
- Country of Publication:
- United States
- Language:
- English
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75 CONDENSED MATTER PHYSICS
SUPERCONDUCTIVITY AND SUPERFLUIDITY
CRYSTAL STRUCTURE
ELECTRIC CONDUCTIVITY
ELECTRICAL PROPERTIES
ELECTROMAGNETIC RADIATION
FAR INFRARED RADIATION
FILMS
GRAIN DENSITY
GRAIN GROWTH
INFRARED RADIATION
JOSEPHSON EFFECT
MICROSTRUCTURE
NIOBIUM COMPOUNDS
NIOBIUM NITRIDES
NITRIDES
NITROGEN COMPOUNDS
PHASE TRANSFORMATIONS
PHYSICAL PROPERTIES
PNICTIDES
RADIATIONS
REFLECTION
SAMPLE PREPARATION
SUPERCONDUCTING FILMS
SUPERCONDUCTIVITY
TRANSITION ELEMENT COMPOUNDS
TRANSMISSION
VERY LOW TEMPERATURE