Structural and electrical transport properties of superconducting (formula presented) films: A random array of superconductor-normal-metal-superconductor Josephson junctions

The structural and superconducting properties of (formula presented) 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 (formula presented) 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 (formula presented) 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 (formula presented) films, all of which were embedded in a uniform (formula presented) matrix. Among these phases, the (formula presented) 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 (formula presented) 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 (formula presented) films is discussed.