Magnetic capping

We investigated the effect of capping three-dimensional topological insulator Bi₂Se₃ with magnetic layers of Cr. We found that the time-reversal symmetry breaking overlayer can induce a gap closing and reopening in the topological surface state as the Cr thickness goes from one to three monolayers. For an odd number of Cr monolayers the preferred direction of the magnetisation is perpendicular to the surface, while for two monolayers the magnetisation of the magnetic film lies in-plane. This spin reorientation transition with film thickness also induces a transition in the spin texture of the topological surface state. For one and three monolayers of Cr the spin texture has a meron structure, while for two monolayers the surface state shows a circular skyrmion spin structure, analogous to that of pristine Bi₂Se₃.

For more details see

Gap and spin texture engineering of Dirac topological states at the Cr−Bi₂Se₃ interface, H. Aramberri and M.C. Muñoz, Phys. Rev. B 93, 245401 (2016).

Preprint available in arXiv, 1602.06829.