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

The coupling of ferroelectric polarization to thin films of the conducting oxide LaNiO₃ results in large changes of conductivity at an epitaxial ferroelectric-LaNiO₃ interface. The observed changes in conductivity are larger than what is expected from band theory, implying the importance of electronic and structural correlations. To characterize the structural changes at the interface, specially designed capacitor structures are fabricated from thin films of PbZr_0.2Ti_0.8O₃ deposited on epitaxial LaNiO₃. The device geometry is optimized for in operando synchrotron x-ray diffraction measurements of crystal truncation rods in order to identify the atomic-scale structural changes responsible for the changes in conductivity. These structural changes include rotations of the LaNiO₃ oxygen octahedra, which are characterized via measurement of half-order Bragg peaks. The octahedral 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 reduced conductivity.