Topological character and magnetism of the Dirac state in Mn-doped Bi2Te3.

First-principles and model calculations show that the Dirac surface state of the topological insulator Bi(2)Te(3) survives upon moderate Mn doping of the surface layers but can lose its topological character as a function of magnetization direction. The dispersion depends considerably on the direction of the Mn magnetization: for perpendicular magnetization, a gap of 16 meV opens up at the Dirac point; for in-plane magnetization, a tiny gap can be opened or closed in dependence on the magnetization azimuth. The ground state is ferromagnetic, with a critical temperature of 12 K.

Complex spin texture in the pure and Mn-doped topological insulator Bi2Te3.

Topological insulators are characterized by the presence of spin-momentum-locked surface states with Dirac points that span the fundamental bulk band gap. We show by first-principles calculations that the surface state of the insulator Bi2Te3 survives upon moderate Mn doping of the surface layers. The spin texture of both undoped and Mn-doped Bi2Te3 is much more complicated than commonly believed, showing layer-dependent spin reversal and spin vortices.