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 BaBiO 3, 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 Sr x Ba 1 − x BiO 3 for x < 0.25, decreasing with an increase in x to reach zero at x = 0.348. This suggests that BaBiO 3 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.