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Mechanism of Charge Transfer across Highly Transparent S-N Interfaces in High Temperature Superconductors
Progress rept. Aug 96-Jul 97
STATE UNIV OF NEW YORK AT STONY BROOK DEPT OF PHYSICS AND ASTRONOMY
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We have studied the influence of various technological parameters irradiation dose, spot size, writing time, etc. on stationary and nonstationary properties of Josephson junctions fabricated by direct electron beam writing and have developed an understanding of the proximity effect and the size and temperature dependence of the Josephson critical current in this type of high-Tc Josephson junctions. Based on the studies of the physical properties of irradiated YBCO films and the defect formation at electron irradiation which were performed during the previous reporting periods, we have developed a quantitative model of the e-beam-made junctions 1. This model takes into account the space distribution of the radiation-induced defects which arises due to the gaussian distribution of the electron density in the incident beam and beam spreading within the film. As a result of this distribution, the interface between the e- beam-damaged and undamaged YBCO is not sharp, and hence the e-beam junctions present an SSNSS structure, where N is a normal metal barrier. This in fact is a highly disordered superconductor in which the critical temperature is strongly suppressed or zero due to a high concentration of radiation-induced pair breaking defects in-plane oxygen vacancies.
APPROVED FOR PUBLIC RELEASE