Low Temperature Metallic State of Ultrathin Films of Bismuth

TL;DR

This study investigates ultrathin amorphous bismuth films, revealing a low-temperature metallic state characterized by temperature-independent resistance below 0.1K, distinct from their higher-temperature behavior, suggesting an intrinsic metallic phase.

Contribution

The paper provides experimental evidence of a low-temperature metallic state in ultrathin amorphous bismuth films, challenging conventional understanding of the superconductor-insulator transition.

Findings

Resistance becomes temperature independent below 0.1K.

Magnetoresistance remains temperature dependent in the same range.

The metallic state is intrinsic, not due to electron cooling failure.

Abstract

Measurements of resistance vs. temperature have been carried out on a sequence of quench-condensed ultrathin films of amorphous bismuth (a-Bi). The resistance below about 0.1K was found to be temperature independent in a range of films with thicknesses spanning the superconductor-to-insulator transition that would be inferred by analyzing data obtained above 0.14K. Film magnetoresistance was temperature dependent in the same temperature range over which the resistance was temperature independent. This implies that the low temperature metallic regime is intrinsic, and not a consequence of failure to cool the electrons.