This work documents the conditions under which the field-tuned behavior of quench condensed films grown on relatively thick layers of a-Sb is essentially identical to that found for amorphous InOx and polycrystalline TiNx films. The electrical transport properties of a series of amorphous Bi (a-Bi) films of different thicknesses, grown with a 14.67 Å thick underlayer of amorphous Sb (a-Sb), were studied in perpendicular and parallel magnetic fields. A magnetoresistance (MR) peak was found in insulating films in both perpendicular and parallel magnetic fields. In all insulating films, Arrhenius type conduction was also found over all ranges of magnetic field. Neither behavior is found for a-Bi films grown on top of thinner a-Sb underlayers, which were substantially smoother. These observations, together with a quantitative analysis of film roughness profiles, highlight the role of mesoscopic scale thickness fluctuations in nucleating superconducting clusters or islands that apparently lead to the MR peak and Arrhenius conduction. This implies that the nature of the disorder plays a major role in determining the character of the insulating regime.
Bibliographical noteFunding Information:
The authors would like to thank Nandini Trivedi, Aviad Frydman and Zvi Ovadyahu for helpful discussions. This work was supported by the National Science Foundation under Grant No. NSF/DMR-1263316. Part of this work was carried out at the University of Minnesota Characterization Facility, a member of the NSF-funded Materials Research Facilities Network via the MRSEC program, and the Nanofabrication Center which receives partial support from the NSF through the NNIN program.
Copyright 2014 Elsevier B.V., All rights reserved.
- Insulating regime
- Superconductor-insulator transitions
- Thin films