Establishing Atomic Coherence in Twisted Oxide Membranes Containing Volatile Elements

Twisted oxide membranes represent a promising platform for exploring moire physics and emergent quantum phenomena. However, the presence of amorphous interfacial dead layers in conventional oxide heterostructures impedes coherent coupling and suppresses moire-induced interactions. While high-temperature thermal treatments can facilitate interfacial bonding, additional care is needed for materials containing volatile elements, where elevated temperatures may cause elemental loss. This study demonstrates the realization of atomically coherent, chemically bonded interface in twisted NaNbO3 heterostructures through controlled oxygen-annealing treatment. Atomic-resolution imaging and spectroscopy reveal ordered perovskite registry accompanied by systematic lattice contraction and modified electronic structure at the twisted interface, providing signatures of chemical reconstruction rather than physical adhesion. This reconstructed interface mediates highly asymmetric strain propagation in which the bottom membrane remains nearly relaxed while the top membrane accommodates substantial shear strain, thereby establishing a strain gradient that enables long-range electromechanical coupling throughout the twisted oxide membranes. By resolving the nature of the reconstructed interface, these findings establish a robust pathway for achieving coherent and strain-tunable oxide moire superlattices, opening pathways to engineer emergent ferroic and electronic functionalities.