Observation of Giant Positive Magnetoresistance in a Cooper Pair Insulator

TL;DR

This study demonstrates a giant positive magnetoresistance in a Cooper pair insulator phase of ultrathin amorphous Bi films, revealing insights into Cooper pair localization and transport mechanisms at low temperatures.

Contribution

It provides experimental evidence of large positive magnetoresistance in a Cooper pair insulator, supporting the existence of this phase in patterned ultrathin films and enhancing understanding of pair localization.

Findings

Magnetoresistance grows exponentially with decreasing temperature

Peak MR occurs at a field sufficient to break Cooper pairs

Resistance transitions to single-electron transport behavior

Abstract

Ultrathin amorphous Bi films, patterned with a nano-honeycomb array of holes, can exhibit an insulating phase with transport dominated by the incoherent motion of Cooper pairs of electrons between localized states. Here we show that the magnetoresistance of this Cooper pair insulator phase is positive and grows exponentially with decreasing temperature, for temperatures well below the pair formation temperature. It peaks at a field estimated to be sufficient to break the pairs and then decreases monotonically into a regime in which the film resistance assumes the temperature dependence appropriate for weakly localized single electron transport. We discuss how these results support proposals that the large MR peaks in other unpatterned, ultrathin film systems disclose a Cooper Pair Insulator phase and provide new insight into the Cooper pair localization.