Nonequilibrium Superconductivity in Optically Illuminated Tunnel Junctions.
HARVARD UNIV CAMBRIDGE MA DIV OF APPLIED SCIENCES
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In the first chapters, the question of what nonequilibrium quasiparticle energy distribution results from optical illumination on a thin film is addressed. A new technique using tunneling current-voltage characteristics is developed which accurately measures the nonequilibrium quasiparticle occupation function, fE. The extremely good resolution of this technique is sufficient to compare the experimental situation to contrasting theoretical models of raised temperature T and shifted electro-chemical potential mu. Data taken on the Al-PbBi tunnel junctions illuminated for this study are well described by the T model. Study of illuminated tunnel junctions lead to the discovery of a new thermoelectric effect for tunneling through oxide barriers between metals at different temperatures. The final chapters are devoted to examination of this thermoelectric effect. Two types of experiments were performed to test for the existence of this effect, with positive results. A self-consistent Rothwarf-Taylor model is presented which correctly predicts the sign, magnitude, temperature dependence and laser-power dependence of the thermoelectric current. The thermoelectric effect described here appears to resolve long-standing discrepancies between experimental results and theoretical predictions for a series of point contact experiments. Author
- Electricity and Magnetism