Observation of bandgap closing in SrxBa1−xBiO3 films: Evidence toward topological order in BaBiO3

Sr x Ba 1 − x BiO 3 (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.