Field-tuned superconductor-insulator transition in BaPb1−xBixO3

Abstract

BaPb${}_{1\ensuremath{-}x}$Bi${}_{x}$O${}_{3}$ is found to exhibit a field-tuned superconductor to insulator transition for Bi compositions 0.24 $\ensuremath{\le}x\ensuremath{\le}$ 0.29. The magnetoresistance of optimally doped samples manifests a temperature-independent crossing point and scaling of the form $\ensuremath{\rho}(T,H)={\ensuremath{\rho}}_{c}F(|H\ensuremath{-}{H}_{c}|{T}^{\ensuremath{-}1/z\ensuremath{\nu}})$, where ${H}_{c}$ is the field determined by the temperature-independent crossing point, and $z\ensuremath{\nu}$ $=$ 0.69 $\ifmmode\pm\else\textpm\fi{}$ 0.03. High-resolution transmission electron microscopy measurements reveal a complex intergrown nanostructure comprising tetragonal and orthorhombic polymorphs. Data are analyzed in terms of both a classical effective medium theory and a field-tuned quantum phase transition, neither of which provides a completely satisfactory explanation for this remarkable phenomenology.