Research Initiation Award: Thermal Boundary Resistance in Thin-Film High-Temperature Superconductors

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ABSTRACT -- CTS 9307753 Phelan The thermal boundary resistance (Rbd) occurring at the interface between high-critical-temperature (high-Tc) superconducting thin films and their substrates plays a major role in determining the operating temperature, and hence the feasibility, of high-Tc superconducting devices. The research objectives are to develop a fundamental understanding of the relationship between the film/substrate interface microstructure and Rbd, and to formulate a model relating Rbd to easily measurable properties like Tc, critical current, and normal-state resistivity. Experiments are performed, using a closed-cycle cryogenic apparatus, on films etched in a novel two-strip meander pattern that enables both normal and superconducting-state measurements to be conducted. Two experimental procedures are proposed. In one, a continuous-wave, visible laser beam serves as a heat source, thus allowing for superconducting-state measurements. In the other, the oxygen content of the high-Tc film is varied so that the film Tc can be controlled, resulting in a normal-state film at temperatures much lower than usual. This allows the two strips to serve as heaters and/or thermometers after a calibration of their electrical resistances versus temperature. The experimental results permit a comparison between Rbd for superconducting-state and normal-state films, and provide valuable information for the thermal design of high-Tc thin-film devices.