Unit-Cell-Thickness Electron Confinement by Geometrically Constrained Antipolar Ordering

Achieving precise electron or spin confinement is essential for the progress of oxide electronics and emerging quantum information processing. While 2D electron confinement is commonly achieved with bare surfaces, heteroepitaxial interfaces, and charged domain walls, its practical application poses challenges, notably by diverse confinement widths, limited material selection, and the lack of freedom of positioning to a desired location within a given material system. Here, with scrutinizing a novel defect structure, the study suggests a new strategy with compelling evidence to trigger electron confinement down to single unit-cell-thickness, through geometrically constrained antipolar ordering facilitated by superlattice-like periodic planar faults in metallic SrFeO3. Employing atomic resolution electron microscopy and density functional theory, the results demonstrate that electrons are confined two-dimensionally to screen the positive bound charges on head-to-head antipolar state boundary, meanwhile oxygen vacancies segregated in the planar faults compensate the negative bound charges on the tail-to-tail one, leading to the stabilization of the antipolar ordering. Additionally, distinguished from traditional methods, this approach offers a potential programing capability for achieving precise charge and spin control by regulating planar fault structure at atomic scale. Unit-cell-thickness 2D electron confinement is realized through geometrically constrained antipolar ordering in metallic SrFeO3. Revealed by atomic resolution electron microscopy and density functional theory, electrons are confined two-dimensionally to screen the positive bound charges on head-to-head antipolar phase boundaries. Meanwhile, oxygen vacancies segregated into planar faults compensate the negative bound charges on the tail-to-tail ones, stabilizing the antipolar ordering state. image