A topological insulator (TI) hosts topologically protected metallic surface states on its boundaries between inner insulating bulk and outer vacuum, and manipulations of its exotic states lead to various interesting phenomena such as quantum anomalous Hall effects and topological magneto-electric couplings. Most studies hitherto have been limited to a specific facet of three-dimensional TI crystals without considering the existence of other surface states on adjacent facets. However, topological surface states of a single TI crystal can exist on all surfaces with different crystal orientations enclosing the crystal and mutual interactions among those contiguous to each other through edges have not yet been examined well. Here we show, based on first-principles electronic structure calculations as well as the theory of the axion electrodynamics, that a net magnetic ordering should be induced on edges between different facets of the three-dimensional TI crystal. In a prototypical TI such as Bi2Se3, the difference in the work function between different crystal-face orientations generates a built-in electric field around facet edges so that lines of effective magnetic dipoles accumulate at those edges for a given broken time-reversal symmetry. The predicted magnetic ordering depending only on the work function differences between facets would be a unique manifestation of the axion electrodynamics in real solids and suggests a route to reveal novel electric and magnetic properties of macroscopic topological edge states of a TI.
Professor Young-Woo Son received his Ph. D. in Physics from Seoul National University in 2004. Then he did postdoc at UC Berkeley and LBNL during 2004-2006. He joined Konkuk University as Assistant Professor in 2007. Then he joined Korea Institute for Advanced Study as Professor in 2008.