We report structural transformation of sixfold vortex domains into two-, four-, and eightfold vortices via a different type of topological defect in hexagonal manganites. Combining high-resolution electron microscopy and Landau-theory-based numerical simulations, we investigate the remarkable atomic arrangement and the intertwined relationship between the vortex structures and the topological defects. The roles of their displacement field, formation temperature, and nucleation sites are revealed. All conceivable vortices in the system are topologically classified using homotopy group theory, and their origins are identified.
Cheng S, Li J, Han M-G, Deng S, Tan G, et al. (2017) Topologically Allowed Nonsixfold Vortices in a Sixfold Multiferroic Material: Observation and Classification. Physical Review Letters 118. Available: http://dx.doi.org/10.1103/physrevlett.118.145501.
The electronic microscopy work was carried out at Brookhaven National Laboratory and supported by the U.S. DOE Basic Energy Sciences, Materials Sciences and Engineering Division under Contract No. DE-SC0012704. J. Z., S.C., and S. D. would like to acknowledge the financial support by Chinese National Natural Science Foundation under Project No. 51390471 and the National 973 Project of China (Project No. 2015CB654902) as well as the support of S. C. for studying abroad from China Scholarship Council. The samples were prepared through the use of the resources of the National Center for Electron Microscopy in Beijing. The theoretic work was done at King Abdullah University of Science and Technology (KAUST) and supported by KAUST Office of Sponsored Research under Grant No. CRF-2015-2549-CRG4.