Granular bismuth 2 strontium 2 calcium copper 2 oxygen 8 (BSCCO) films were prepared by laser ablation and postannealing followed by deoxygenation to vary the grain boundary properties. A detailed study was made of the fast nonlinear photoresponse of these films with emphasis on modelling and magnetic effects. Measurements of the sensitivity as a function of temperature, bias current and intensity reveal the signal source to be nonbolometric. The response is found to obey a square root law. It is believed that the detection mechanism arises from the interaction of rain boundary Josephoon junctions with radiation induced screening currents.
Spray pyrolysis was investigated as a method of production of superconducting films of the BSCCO family. The process variables which govern deposition were identified and the properties of the sprayed films were determined.
The optical properties of high temperature superconductors (HTS) in thin film form under high power for infrared (FIR) radiation has been investigated. Several kinds of infrared response were observed based on different physical mechanisms. High critical temperature films showed a resistance response in a current biased mode like photoconductors. Photovoltaic signals were detected in both the superconducting and the normal conducting phase of thin films of yttrium barium2 copper 3 oxygen (7-x).
Below the critical temperature a voltage signal is generated if the sample is subjected to a small magnetic field parallel to the plane of the film. This effect has been attributed to an infrared induced Nernst effect in thallium 2 barium 2 calcium copper 2 oxygen 8 films.
Above the critical temperature strong voltage signals occur in ab oriented films which have a slight misalingment in crystallographic orientation which generates a kind of atomic layer thermocouple yielding a very large effect.
High temperature superconductors have an energy gap which can be observed in the far infrared. We intend to deposit and characterise superconducting oxides on a FIR transparent substrate, and perform linear and nonlinear spectroscopy. Such techniques will allow to elucidate the processes involved in HTC superconductors and open the area of ultrahigh frequency parallel devices analogous to optical computers