Observation of bandgap closing in Sr_xBa_1−xBiO₃ films: Evidence toward topological order in BaBiO₃

$SrxBa1−xBiO3$ (⁠$0≤x<0.5$⁠) films were fabricated from solution-phase precursors using flow-limited field-injection electrostatic spraying to investigate the predicted topological properties of $BaBiO3$⁠, an oxide perovskite. The films were analyzed via x-ray diffraction, optical conductivity, and Raman spectroscopy. The bandgaps measured by optical absorption spectroscopy were in line with the predicted value of $SrxBa1−xBiO3$ for $x<0.25$⁠, decreasing with an increase in $x$ to reach zero at $x=0.348$⁠. This suggests that $BaBiO3$ may have topological order and that, upon appropriate doping, it may be used as a topological insulator or superconductor in quantum-computing devices. This work may open up new avenues toward engineering of topological insulators with precise and reproducible control of stoichiometry, obviating extreme deposition temperatures or vacuum processing.