Structural and electrical transport properties of superconducting Au_0.7In_0.3 films: A random array of superconductor-normal-metal-superconductor Josephson junctions

The structural and superconducting properties of Au_0.7In_0.3 films, grown by interdiffusion of alternating Au and In layers, have been studied. The films were found to consist of a uniform solid solution of Au_0.9In_0.1, with excess In precipitated in the form of In-rich grains of various Au-In phases with distinct atomic compositions, including intermetallic compounds. As the temperature was lowered, these individual grains became superconducting at a particular local transition temperature (T⁰_c), determined primarily by the atomic composition of the grain, before a fully superconducting state of zero resistance was established. From the observed onset temperature of the superconducting transition, it was inferred that up to three different superconducting phases could have formed in these Au_0.7In_0.3 films, all of which were embedded in a uniform Au_0.9In_0.1 matrix. Among these phases, the T⁰_c of a particular one, 0.8 K, is higher than any previously reported for the Au-In system. The electrical transport properties were studied down to low temperatures. The transport results were found to be well correlated with those of the structural studies. The present work suggests that these Au_0.7In_0.3 films can be modeled as a random array of superconductor-normal-metal-superconductor Josephson junctions. The effect of disorder and magnetic field on the superconducting transition in these Au_0.7In_0.3 films is discussed.