Coherent-strained superconducting BaPb1−xBixO3 thin films by interface engineering

Abstract

The bismuthate superconductor $\mathrm{BaP}{\mathrm{b}}_{1\ensuremath{-}x}\mathrm{B}{\mathrm{i}}_{x}{\mathrm{O}}_{3}$ and its bismuthate heterostructure have gained much attention due to their potential applications, such as topologically protected quantum devices. To fabricate $\mathrm{BaP}{\mathrm{b}}_{1\ensuremath{-}x}\mathrm{B}{\mathrm{i}}_{x}{\mathrm{O}}_{3}$-based junctions or devices with atomically sharp interfaces, researchers have long searched for innovative methods to achieve coherent-strained superconducting $\mathrm{BaP}{\mathrm{b}}_{1\ensuremath{-}x}\mathrm{B}{\mathrm{i}}_{x}{\mathrm{O}}_{3}$ films. However, the large lattice mismatches between $\mathrm{BaP}{\mathrm{b}}_{1\ensuremath{-}x}\mathrm{B}{\mathrm{i}}_{x}{\mathrm{O}}_{3}$ and widely used perovskite substrates have been huge obstacles hindering the achievement of coherent-strained superconducting films. Here, we successfully fabricated coherent-strained superconducting $\mathrm{BaP}{\mathrm{b}}_{1\ensuremath{-}x}\mathrm{B}{\mathrm{i}}_{x}{\mathrm{O}}_{3}$ films on $\mathrm{SrTi}{\mathrm{O}}_{3}$ substrates by inserting $\mathrm{BaCe}{\mathrm{O}}_{3}/\mathrm{BaZr}{\mathrm{O}}_{3}$ buffer layers. By performing both grazing-incidence in-plane x-ray diffraction and transmission electron microscopy, we demonstrated that without buffer layers the $\mathrm{BaP}{\mathrm{b}}_{1\ensuremath{-}x}\mathrm{B}{\mathrm{i}}_{x}{\mathrm{O}}_{3}$ films exhibited fully relaxed structures with a reconstructed interface layer. With buffer layers, the superconducting transition temperatures of coherent-strained $\mathrm{BaP}{\mathrm{b}}_{1\ensuremath{-}x}\mathrm{B}{\mathrm{i}}_{x}{\mathrm{O}}_{3}$ films were higher than that of relaxed films. Based on these interface-engineering results, this paper provides opportunities for exploring the emergent properties of bismuthate-based superconducting devices, such as quantum computing circuits.