Structural Reconstructions at Bismuthate/Titanate Interfaces

Perovskite hole-doped bismuthates exhibits a superconducting transition up to 32 K while the parent material are insulating due to a charge density wave associated with a structural breathing mode distortion of the oxygen octahedra. To suppress the distortion, we investigate the structural properties of BaBiO₃/LaTiO₃ and BaBiO₃/BaTiO₃ interfaces using a combination of synchrotron X-ray scattering measurements and Raman spectroscopy. We find that a structural resonstruction of at the BaBiO₃/LaTiO₃ interface leads to the formation of a Ruddleson-Popper type phase. This reconstruction is suppressed in BaBiO₃/BaTiO₃ heterostructures where ferroelectricity in heterostructures with 4 unit cells of BaBiO₃. Raman measurements confirm the suppression of the vibrational mode associated with the breathing mode distortion. The coupling between the ferroelectric polarization and the electronic states in BaBiO₃ may potentially serve as a starting point for tunable electrostatic doping to realize the novel predicted states in the atomically-thin BaBiO₃ layers.