SUPERCONDUCTING PROXIMITY EFFECT THROUGH HIGH-QUALITY HIGH-CONDUCTANCE TUNNEL BARRIERS

The temperature dependence of the critical current of very high-conduc tance Nb-AlOx-Al-AlOx-Nb tunnel junctions with thin middle Al layers ( thickness d(Al) 2-8 nm) shows a tail above the Al critical temperature , whose amplitude strongly depends on d(Al). This is interpreted as ev idence of a proximity effect through tunnel barriers whose high qualit y and transparency can be independently assessed. These data have been modeled within the framework of the McMillan model using independentl y measurable barrier transmission factors, and obtaining an excellent quantitative agreement.