Homotopy-Theoretic Study &atomic-Scale Observation of Vortex Domains in Hexagonal Manganites

Abstract

Essential structural properties of the non-trivial "string-wall-bounded" topological defects in hexagonal manganites are studied through homotopy group theory and spherical aberration-corrected scanning transmission electron microscopy. The appearance of a "string-wall-bounded" configuration in RMnO 3 is shown to be strongly linked with the transformation of the degeneracy space. The defect core regions (∼50 Å) mainly adopt the continuous U(1) symmetry of the higherature phase, which is essential for the formation and proliferation of vortices. Direct visualization of vortex strings at atomic scale provides insight into the mechanisms and macro-behavior of topological defects in crystalline materials.