Electromagnetic spin polarization on the surface of topological insulator

Abstract

We study the spin polarization of the electrons on the surface of topological insulators under a dc electric field or a circularly polarized light by using Keldysh Green's function formalism. When a dc electric field Ex ∼ 10 3 V/m is applied, a spin polarization σy ≃ 5.2 × 10 −8Å−2 is induced. Furthermore, we also find that a light illumination induces the out-of-plane component of the spin polarization as a result of the inverse Faraday effect. The magnitude of the spin polarization is proportional to the square of the lifetime τ and σz ≃ 2 × 10 −10Å−2 for typical parameters. Finally, we investigate the spin polarization in the presence of the warping term. By the symmetry consideration of the system, we find that the out-of-plane spin polarization is cubic of the current and that the magnitude of the induced spin polarization depends on the direction of the applied current.

Optically tunable spin transport on the surface of a topological insulator

“…Since the discovery of topological insulators (TI) [1][2][3][4][5][6] followed by unprecedented research activity in the field there has been a tremendous interest in studying their unique spin properties [7][8][9][10][11][12][13][14]. The phenomenon which is called topological protection makes it harder to destroy the quantum phase coherence of conducting electrons propagating at the surface.…”

Magneto-optical Faraday and Kerr effects in topological insulator films and in other layered quantized Hall systems

“…Because topological insulators (TIs) have gapless helical surface states [1][2][3][4] that respond strongly to timereversal symmetry breaking perturbations, magnetooptical studies have emerged as an important tool for their characterization [5][6][7][8][9][10][11][12][13][14][15] . This paper expands on previous work 10,11 in which we demonstrated that ideal TIs exhibit striking unversal features in their long-wavelength response -a universal Faraday angle equal to the fine structure constant and a giant 90 degrees Kerr rotation.…”

Spin-dependent phenomena in semiconductors in strong electric fields

“…where c is a dimensionless coefficient of the order of unity, v and p are the root-mean-squares of the group velocity and the quasimomentum referred to the extremum point in the Brillouin zone, p dr is the electron drift momentum in the electric field E and β so is a coefficient (in units of velocity) relating the spin-orbit energy to the electron quasimomentum. The value of the induced spin s can be increased by increasing the ratios β so /v and (or) p dr / p. The first ratio is large and has an order of unity in strongly spin-orbit coupled systems, like p-type bulk Te, the (111) surface of topological insulator Bi 2 Se 3 [16][17][18] and new classes of noncentrosymmetric systems that emerged recently [19]. However, in this case, the spin is tightly bound to the quasimomentum and loses the degree of freedom.…”