Establishing Atomic Coherence in Twisted Oxide Membranes Containing Volatile Elements

Twisted oxide membranes represent a promising platform for exploring moiré physics and emergent quantum phenomena. However, the presence of amorphous interfacial "dead" layers in conventional oxide heterostructures impedes coherent coupling and suppresses moiré-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 an atomically coherent, chemically bonded interface in twisted NaNbO₃ membranes 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. By resolving the nature of the reconstructed interface, these findings establish a pathway for achieving coherent and strain-tunable oxide moiré superlattices.