Structural and electrical transport properties of superconducting Au{0.7}In{0.3} films: A random array of superconductor-normal metal-superconductor (SNS) Josephson junctions

摘要

The structural and superconducting properties of Au{0.7}In{0.3} films, grownby interdiffusion of alternating Au and In layers, have been studied. The filmswere found to consist of a uniform solid solution of Au{0.9}In{0.1}, withexcess In precipitated in the form of In-rich grains of various Au-In phases(with distinct atomic compositions), including intermetallic compounds. As thetemperature was lowered, these individual grains became superconducting at aparticular transition temperature (Tc), determined primarily by the atomiccomposition of the grain, before a fully superconducting state of zeroresistance was established. From the observed onset Tc, it was inferred that upto three different superconducting phases could have formed in theseAu{0.7}In{0.3} films, all of which were embedded in a uniform Au{0.9}In{0.1}matrix. Among these phases, the Tc of a particular one, 0.8 K, is higher thanany previously reported for the Au-In system. The electrical transportproperties were studied down to low temperatures. The transport results werefound to be well correlated with those of the structural studies. The presentwork suggests that Au{0.7}In{0.3} can be modeled as a random array ofsuperconductor-normal metal-superconductor (SNS) Josephson junctions. Theeffect of disorder and the nature of the superconducting transition in theseAu{0.7}In{0.3} films are discussed.