Atomistic Defect Makes a Phase Plate for the Generation and High-Angular Splitting of Electron Vortex Beams

摘要

Topological defects in solid-state materials by breaking the translational symmetry offer emerging properties that are not present in their parental phases. For example, edge dislocations-the 2 pi phase-winding topological defects-in antiferromagnetic NiO crystals can exhibit ferromagnetic behaviors. Herein, we study how these defects could give rise to topological orders when they interact with a high-energy electron beam. To probe this interaction, we formed a coherent electron nanobeam in a scanning transmission electron microscope and recorded the far-field transmitted patterns as the beam steps through the edge dislocation core in [001] NiO. Surprisingly, we found the amplitude patterns of the < 020 > Bragg disks evolve in a similar manner to the evolution of an annular solar eclipse. Using the ptychographic technique, we recovered the missing phase information in the diffraction plane and revealed the topological phase vortices in the diffracted beams. Through atomic topological defects, the wave function of electrons can be converted from plane wave to electron vortex. Technologically, this approach provides a feasible route for the fabrication of phase plates that can generate electron vortex beams with an angular separation that is 3 orders of magnitude larger than what traditional nanofabrication technology can offer. This advance will enable the collection of magnetic circular dichroism spectra with high spatial resolution and high efficiency, boosting the understanding of the relationship between symmetry breaking and magnetic property of individual topological defect at the atomic scale.