Interfacial mechanical coupling at the interface of Pb_0.2Zr_0.8TiO₃/LaNiO₃/SrTiO₃ heterostructures

The coupling of ferroelectric polarization to the conducting oxide LaNiO₃ results in large changes of the conductivity at an epitaxial ferroelectric-LaNiO₃ interface. Systematic measurements of the conductivity with varying LaNiO₃ conducting channel thickness show that the effect is confined to within a few atomic layers of the interface. We correlate changes in conductivity with structural changes in the ferroelectric and conducting oxide as the ferroelectric polarization is switched through in operando synchrotron diffraction measurements. We observe changes in the tetragonality and displacement of the transition metal cations and oxygen anions in both Pb_0.2Zr_0.8TiO₃ and LaNiO₃. We also characterize rotations of oxygen octahedra in LaNiO₃ via measurement of half order Bragg peaks. These rotations exhibit a hysteresis loop as the applied voltage is swept through the coercive field of the ferroelectric and are correlated with the conductivity of the channel, with larger rotations leading to smaller conductivity. The observed changes in conductivity are larger than that expected from band theory alone, implying a large role of electronic correlations. By using the ferroelectric to effect changes in the structure, we explore the correlated transport behavior of LaNiO₃ in new ways.