Twistronics with oxide membranes

Place: conference room, IMDEA Nanociencia.

Abstract:

The realization of freestanding perovskite-oxide membranes has enabled their deterministic mechanical assembly into twisted homo-bilayers, overcoming the constraints of epitaxial growth that rigidly lock crystallographic orientation to a substrate. In contrast to van der Waals systems, twisted oxide membranes form interfaces governed by strong long-range ionic bonding in a non-coherent atomic registry, leading to pronounced interface reconstruction and the emergence of unconventional moiré strain fields. In ferroelectric membranes, these reconstructed interfaces introduce a controllable chirality degree of freedom, providing a powerful route to engineer topological polar textures governed by lateral strain modulations imposed by twist geometry.In this talk, I will focus on how interface reconstruction and relaxation mechanisms unique to freestanding membranes shape the resulting strain and polarization landscapes. Using CO₂ laser annealing, we reveal relaxation pathways that drive ripple formation and interface reconstructions distinct from those observed in coherently bonded crystalline interfaces. To further probe the strength and range of interlayer coupling, we investigate twisted bilayers separated by graphene spacers. While graphene partially screens the interfacial atomic potential and suppresses detectable strain signatures—analogous to remote epitaxy—robust ferroelectric vortex arrays persist for spacer thicknesses up to several nanometres, indicating a regime of remote moiré interaction.Finally, I will address whether such reconstructed interfaces can induce polar topology in nominally non-ferroelectric materials. Focusing on twisted SrTiO₃ bilayers, a quantum paraelectric, I will show that non-uniform moiré strains stabilize polarization vortex arrays. Density-functional calculations reproduce the experimental observations and identify a flexoelectrically driven polar state associated with an anomalously large negative flexoelectric coefficient. These results establish interface reconstruction in twisted oxide membranes as a key design principle for creating and controlling emergent polar and topological states

References:[1] G. Sanchez-Santolino et al. Nature 626, 529 (2024)

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