Flexoelectricity in thin films and membranes of complex oxides

Flexoelectricity describes the generation of electric polarization in response to inhomogeneous strain, i.e., strain gradient, in all dielectrics. Importantly, strain gradients are inversely scaled to the material dimension so that more prominent and exotic phenomena can be envisioned at the nanoscale, based on flexoelectricity. In particular, in complex oxides, such a large lattice inhomogeneity can also host a rich spectrum of properties and functionalities, via a subtle interplay with charge, spin, and orbital. Here, motivated by advances in nanoscale thin-film and membrane syntheses of complex oxides, we present the frontiers and challenges of flexoelectricity. Together with the advanced synthesis techniques, state-of-the-art experimental nano-techniques will continue to reveal hitherto hidden functionalities through flexoelectricity. Meanwhile, further breakthroughs in the research of flexoelectricity will require consistency between theory and experiment and will rely on the versatile exploitation of large strain gradients in nanoscale complex oxides.