Nonequilibrium spin texture within a thin layer below the surface of current-carrying topological insulator Bi${}_2$Se${}_3$: A first-principles quantum transport study

Abstract

We predict that unpolarized charge current injected into a ballistic thin film of prototypical topological insulator (TI) Bi${}_2$Se${}_3$ will generate a {\it noncollinear spin texture} $\mathbf{S}(\mathbf{r})$ on its surface. Furthermore, the nonequilibrium spin texture will extend into $\simeq 2$ nm thick layer below the TI surfaces due to penetration of evanescent wavefunctions from the metallic surfaces into the bulk of TI. Averaging $\mathbf{S}(\mathbf{r})$ over few Å along the longitudinal direction defined by the current flow reveals large component pointing in the transverse direction. In addition, we find an order of magnitude smaller out-of-plane component when the direction of injected current with respect to Bi and Se atoms probes the largest hexagonal warping of the Dirac-cone dispersion on TI surface. Our analysis is based on an extension of the nonequilibrium Green functions combined with density functional theory (NEGF+DFT) to situations involving noncollinear spins and spin-orbit coupling. We also demonstrate how DFT calculations with properly optimized local orbital basis set can precisely match putatively more accurate calculations with plane-wave basis set for the supercell of Bi${}_2$Se${}_3$.

5 pages, 4 figures, PDFLaTeX

References in corpus (6)

• Current induced electron spin polarization in strained semiconductors
• Electrical detection of the spin polarization due to charge flow in the surface state of the topological insulator Bi_1.5 Sb_0.5 Te_1.7 Se_1.3
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• Spin-transfer torque and spin-polarization in topological-insulator/ferromagnet vertical heterostructures
• Robustness of the helical edge states in topological insulators
• Ab-initio transport across Bismuth Selenide surface barriers

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