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

The bismuthate superconductor BaPb1-xBixO3 and its bismuthate heterostructure have gained much attention due to their potential applications, such as topologically protected quantum devices. To fabricate BaPb1-xBixO3-based junctions or devices with atomically sharp interfaces, researchers have long searched for innovative methods to achieve coherent-strained superconducting BaPb1-xBixO3 films. However, the large lattice mismatches between BaPb1-xBixO3 and widely used perovskite substrates have been huge obstacles hindering the achievement of coherent-strained superconducting films. Here, we successfully fabricated coherent-strained superconducting BaPb1-xBixO3 films on SrTiO3 substrates by inserting BaCeO3/BaZrO3 buffer layers. By performing both grazing-incidence in-plane x-ray diffraction and transmission electron microscopy, we demonstrated that without buffer layers the BaPb1-xBixO3 films exhibited fully relaxed structures with a reconstructed interface layer. With buffer layers, the superconducting transition temperatures of coherent-strained BaPb1-xBixO3 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.