  We report the observation of a quantum phase transition (QPT), tuned by a
parallel magnetic field, between a superconducting and metallic state in
Au0.7In0.3 films of very low normal-state sheet resistance (< 90 Ohms). These
films can be modeled as a random array of superconductor-normal
metal-superconductor (SNS) junctions. Electrical transport and tunneling
measurements suggest that, in the metallic state, the film consists of
superconducting In-rich grains not linked by Josephson coupling. Whether phase
fluctuation, which is not expected to be strong in such an SNS junction system
according to the phase-number uncertainty relation, or a different physical
process drives the observed QPT is discussed.
