Cooper Pair Insulator phase induced in amorphous Pb$_0.9$Bi$_0.1$ thin films

TL;DR

This paper demonstrates that a Cooper pair insulator phase can be induced in amorphous Pb$_{0.9}$Bi$_{0.1}$ thin films by substrate-induced nanoscale thickness variations, confirming the substrate's role in Cooper pair localization.

Contribution

It shows that the CPI phase develops in Pb-Bi films on nano-porous substrates, extending the understanding of substrate influence on Cooper pair localization.

Findings

CPI phase appears in Pb-Bi films on nano-porous substrates.

Substrate structure influences Cooper pair localization.

CPI phase can be induced in various superconducting materials.

Abstract

A Cooper pair insulator (CPI) phase emerges near the superconductor-insulator transitions of a number of strongly-disordered thin film systems. Much recent study has focused on a mechanism driving the underlying Cooper pair localization. We present data showing that a CPI phase develops in amorphous Pb$_{0.9}$Bi$_{0.1}$ films deposited onto nano-porous anodized aluminum oxide surfaces just as it has been shown to develop for a-Bi films. This result confirms the assertion that the CPI phase emerges due to the structure of the substrate. It supports the picture that nanoscale film thickness variations induced by the substrate drive the localization. Moreover, it implies that the CPI phase can be induced in any superconducting material that can be deposited onto this surface.