Application of Diffuse Mismatch Theory to the Prediction of Thermal Boundary Resistance in Thin-Film High-T_c Superconductors

Thermal boundary resistance (R_b) plays an important role in the design and performance of thin-film high-temperature superconducting devices, such as infrared detectors and optical switches, which rely upon the temperature rise of the film as the basis for their operation. Although there is general agreement on the magnitude of R_b from experimental data, there is at present no generally accepted theory capable of predicting R_b for these films, particularly at the intermediate cryogenic temperatures where they are likely to be used. Here, the Diffuse Mismatch Model (DMM), which considers that all phonons reaching the interface between the film and substrate scatter diffusely, is applied to the calculation of R_b. The results indicate that although the DMM yields results slightly more in agreement with data than the Acoustic Mismatch Model (AMM), the experimental data lie far above the calculated values. Removing the assumptions involved in the derivation of the DMM in some cases improves the agreement with the experimental data, but additional features must be incorporated into the model to achieve quantitative agreement between theory and experiment.