Anomalous absorption in granular superconductors

Thesis/Dissertation · Fri Jan 01 04:00:00 EST 1982

OSTI ID:5685935

Carr, G L

This dissertation is concerned with the far infrared properties of granular superconductors. Two granular systems were studied: composites of metal grains imbedded in an insulator and granular metal films on insulating substrates. The metals studied were Sn, Pb and Nb. Infrared transmission measurements were made with the metal grains in the superconducting state and in the normal state. For the composites, the normal state absorption was found to be several orders of magnitude larger than simple theoretical predictions. Further, the composites were more absorbing in the superconducting state than in the normal state at frequencies around the superconducting energy gap. The magnitude of this absorption increase was found to scale with the overall normal state absorption. A simple model for a small particle composite incorporating the response of a superconductor into the average field theory for the composites predicts that the absorption be reduced when the grains are superconducting. This model is in direct contradiction to the experimental results. Similarly, when the thin films were composed of small isolated grains, there was an increase in absorption at the gap frequency. The transmittance of these films in the normal state was high and frequency dependent. When the grains in the film were more extended and less isolated from one another, the normal state transmission was low and frequency independent; the absorption near the gap for the superconducting state was less than for the normal state, in accord with theory. The results of this investigation suggest that the response of very small, isolated superconductors is very much different from the bulk. No clear explanation for this anomalous absorption increase for very granular superconductors is presently available.

• Research Organization: Ohio State Univ., Columbus (USA)
• OSTI ID: 5685935
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
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& Thermal Phenomena-- (-1987)
75 CONDENSED MATTER PHYSICS
SUPERCONDUCTIVITY AND SUPERFLUIDITY
COMPOSITE MATERIALS
CRYSTAL STRUCTURE
ELECTROMAGNETIC RADIATION
ELEMENTS
GRAIN ORIENTATION
INFRARED RADIATION
LEAD
MATERIALS
METALS
MICROSTRUCTURE
NIOBIUM
OPTICAL PROPERTIES
ORIENTATION
PHYSICAL PROPERTIES
PHYSICAL RADIATION EFFECTS
RADIATION EFFECTS
RADIATIONS
SUPERCONDUCTING COMPOSITES
TIN
TRANSITION ELEMENTS