Cooper pair insulator in amorphous films induced by nanometer-scale thickness variations

Abstract

Unusual transport properties of superconducting (SC) materials, such as the under doped cuprates, low dimensional superconductors in strong magnetic fields, and insulating films near the Insulator Superconductor Transition (IST), have been attributed to the formation of inhomogeneous phases. Difficulty correlating the behaviors with observations of the inhomogeneities make these connections uncertain. Of primary interest here are proposals that insulating films near the IST, which show an activated resistance and giant positive magnetoresistance, contain islands of Cooper Pairs (CPs). Here we present evidence that these types of inhomogeneities are essential to such an insulating phase in amorphous Bi (a-Bi) films deposited on substrates patterned with nanometer-sized holes. The patterning induces film thickness variations, and corresponding coupling constant variations, that transform the composition of the insulator from localized electrons to CPs. Analyses near the thickness-tuned ISTs of films on nine different substrates show that weak links between SC islands dominate the transport. In particular, the ISTs all occur when the link resistance approaches the resistance quantum for pairs. These observations lead to a detailed picture of CPs localized by spatial variations of the superconducting coupling constant.

4 pages, 3 figures, 1 supplemental page with 1 supplemental figure

References in corpus (9)

• Localization of preformed Cooper-pairs in disordered superconductors
• Nature of the superconductor-insulator transition in disordered superconductors
• Disorder-Induced Inhomogeneities of the Superconducting State Close to the Superconductor-Insulator Transition
• Eigenfunction fractality and pseudogap state near superconductor-insulator transition
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• Observation of Giant Positive Magnetoresistance in a Cooper Pair Insulator
• Scale dependent superconductor-insulator transition
• Nanopattern-stimulated superconductor-insulator transition in thin TiN films
• Cooper pairs under the action of disorder and strong magnetic field

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