Superconductivity-localization interplay and fluctuation magnetoresistance in epitaxial BaPb$_{1-x}$Bi$_x$O$_3$ thin films

TL;DR

This study investigates the interplay of superconductivity, localization, and fluctuations in epitaxial BaPb$_{1-x}$Bi$_x$O$_3$ thin films, revealing extended fluctuation regions and the effects of disorder and dimensionality on superconducting properties.

Contribution

It provides new insights into superconducting fluctuations and the superconductor-insulator transition in BaPb$_{1-x}$Bi$_x$O$_3$ thin films, highlighting the role of disorder and film thickness.

Findings

Superconducting fluctuations extend well above $T_c$ in thick films.

Decreasing film thickness induces a superconductor-insulator transition.

Disorder correlates strongly with the observed $T_c$.

Abstract

BaPb$_{1-x}$Bi$_x$O$_3$ is a superconductor, with transition temperature $T_c=11$ K, whose parent compound BaBiO$_3$ possess a charge ordering phase and perovskite crystal structure reminiscent of the cuprates. The lack of magnetism simplifies the BaPb$_{1-x}$Bi$_{x}$O$_3$ phase diagram, making this system an ideal platform for contrasting high-$T_c$ systems with isotropic superconductors. Here we use high-quality epitaxial thin films and magnetotransport to demonstrate superconducting fluctuations that extend well beyond $T_c$. For the thickest films (thickness above $\sim100$ nm) this region extends to $\sim27$ K, well above the bulk $T_c$ and remarkably close to the higher $T_c$ of Ba$_{1-x}$K$_x$BiO$_3$ ($T_c=31$ K). We drive the system through a superconductor-insulator transition by decreasing thickness and find the observed $T_c$ correlates strongly with disorder. This material manifests strong fluctuations across a wide range of thicknesses, temperatures, and disorder presenting new opportunities for understanding the precursor of superconductivity near the 2D-3D dimensionality crossover.