ELECTRONIC-PROPERTIES AND SUPERCONDUCTIVITY OF AMORPHOUS SI1-XAUX ALLOYS NEAR THE METAL-INSULATOR-TRANSITION

We report on specific-heat and resistivity measurements on quench-condensed Si1-xAux films for 0.11 less than or equal to x less than or equal to 0.36 in the temperature range 0.35 K less than or equal to T less than or equal to 6 K. A distinct increase of the specific-heat derived electronic density of states at the Fermi level is observed at x(b) approximate to 0.2, i.e., in the vicinity of the metal-insulator transition occurring for our samples at x(c) = 0.16. This suggests a different type of bonding between Au and Si for x<x(b) and x>x(b). While resistive transitions to superconductivity are observed for x greater than or equal to 0.21, the absence of a specific-heat anomaly at the transition points to filamentary superconductivity except for x = 0.35 where a sizable anomaly is seen. The difference in various electronic properties between differently prepared samples of these metastable alloys, in particular the influence of different preparation and annealing temperatures is emphasized. It is suggested that these differences are caused by incipient phase separation in the room-temperature prepared samples.