A spin density wave in the topological insulator Bi2Te3

Topological insulators are materials with a bulk band gap, but with topologically protected, spin polarized surface states with Dirac dispersion. Bi2Te3 is such a topological insulator with a single Dirac cone at the center of the Brillouin zone. ARPES studies have shown that the Fermi surface of Bi2Te3 changes from a circle to a hexagon, and then to a hexagram, when moving away from the Dirac point. This has been explained in literature by the addition of a warping term added to the Dirac Hamiltonian, which leads to more exotic spin texture. This manuscript elaborates on hexagonal warping in Bi2Te3, and examines a possible spin density wave (SDW) state due to warping. Using Landau– Ginzburg formalism, we find that a correspondence between the SDW state and the cubic anisotropy problem. Using this, we construct a phase diagram of spin order in on the hexagonal Fermi surface of Bi2Te3.