ELECTRON-TUNNELING STUDIES OF ULTRATHIN FILMS NEAR THE SUPERCONDUCTOR-TO-INSULATOR TRANSITION

Electron tunneling measurements on ultrathin quench-condensed films ne ar the superconductor-to-insulator (SI) transition reveal that the sup erconducting state degrades with increasing normal state sheet resista nce, R(square), in a manner that depends strongly on film morphology. In homogeneously disordered films, the superconducting energy gap DELT A0 decreases continuously and appears to go to zero at the SI transiti on. In granular films the transport properties degrade while DELTA0 re mains constant. Measurements in the normal state reveal disorder enhan ced e--e-interaction corrections to the density of states. These effec ts are strong and depend on morphology in a manner that is consistent with their playing an important role in driving the SI transition.