Helical States of Topological Insulator Bi2Se3

We report density functional theory analysis of the electronic and quantum transport properties of Bi2Se3 topological insulator, focusing on the helical surface states at the Fermi level E-F. The calculated Dirac point and the tilt angle of the electron spin in the helical states are compared quantitatively with the experimental data. The calculated conductance near E-F shows a V-shaped spectrum, consistent with STM measurements. The spins in the helical states at E-F not only tilts out of the two-dimensional plane, they also oscillate with a 3-fold symmetry going around the two-dimensional Brillouin zone. The helical states penetrate into the material bulk, where the first quintuple layer contributes 70% of the helical wave functions.