Spin Polarization and Transport of Surface States in the Topological InsulatorsBi2Se3andBi2Te3from First Principles

Abstract

We investigate the band dispersion and the spin texture of topologically protected surface states in the bulk topological insulators Bi2Se3 and Bi2Te3 by first-principles methods. Strong spin-orbit entanglement in these materials reduces the spin polarization of the surface states to ∼50% in both cases; this reduction is absent in simple models but of important implications to essentially any spintronic application. We propose a way of controlling the magnitude of spin polarization associated with a charge current in thin films of topological insulators by means of an external electric field. The proposed dual-gate device configuration provides new possibilities for electrical control of spin.

Observation of a highly spin-polarized topological surface state in GeBi2Te4

“…Also, the surface spin polarization needs to be as high as possible even though its magnitude is predicted to be reduced to 50%-60% for Bi 2 Se 3 and Bi 2 Te 3 due to inevitable spin and orbital entanglement. 36 Although the topological surface state was experimentally identified, 34 such important information on these aspects in the presence of mixed interlayers is so far missing for GeBi 2 Te 4 . Here, we report that the Dirac point of the TSS is located within the bulk band gap of ∼180 meV and that the TSS has a substantial spin polarization of ∼70%, which is revealed by means of spin-resolved/integrated ARPES.…”

Electrical Detection of Spin-Polarized Surface States Conduction in (Bi0.53Sb0.47)2Te3 Topological Insulator

“…This is smaller than the theoretical predication of about 50% spin polarization for the 3D TI surface states from first-principle calculations. 21 Such deviation can be probably attributed to that the dimension of the top surface in our device (in micron scale) is much larger than the typical mean-free path and phase coherence length (tens to hundreds nanometers, see Supporting Information S10), 17,18,37 hence the carrier transport through the surface states suffers from considerable scatterings. Another possible reason could be the overestimation of the spin detection efficiency in the nonideal Co/Al 2 O 3 tunneling contact, considering that the (Bi 0.53 Sb 0.47 ) 2 Te 3 surface has a terracelike morphology.…”

“…Because of the strong spin−orbital interaction in TI, direct back scatterings from nonmagnetic impurities are prohibited by the time-reversal symmetry. 8,9 More importantly, the spin-momentum locking naturally leads to a currentinduced spin polarization in surface states; 21 the surface states conduction is spin-polarized once an electric current is passed through a TI film, and this spin polarization can be accordingly reversed by simply flipping the electric current direction. 22,23 As a result, it has been proposed to use TI as a promising spin injection source to inject spin-polarized carriers into nonmagnetic materials, such as metal and graphene.…”

Aharonov–Bohm oscillations in a quasi-ballistic three-dimensional topological insulator nanowire

“…I n three-dimensional topological insulator (3D TI) nanowires, charge transport occurs via gapless surface states where the spin is fixed perpendicular to the momentum [1][2][3][4][5][6] . When a magnetic field (B) is applied along the nanowire axis, the surface electrons encircling the wire pick up a phase of 2pF/F 0 , where F ¼ BS is the magnetic flux through cross-sectional area S and F 0 ¼ h/e is the magnetic flux quantum, where h is Planck's constant and e the electron charge.…”