Triangular growth spirals on a Bi₂Se₃ film imaged via scanning tunneling microscopy.

From the article:

Charging Dirac States at Antiphase Domain Boundaries in the Three-Dimensional Topological Insulator ${\mathrm{Bi}}_2{\mathrm{Se}}_3$
Y. Liu, Y. Y. Li, D. Gilks, V. K. Lazarov, M. Weinert, and L. Li
Phys. Rev. Lett. 110, 186804 (2013)

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