Spin Hall photoconductance in a three-dimensional topological insulator at room temperature

Abstract

Three-dimensional topological insulators are a class of Dirac materials, wherein strong spin-orbit coupling leads to two-dimensional surface states. The latter feature spin-momentum locking, i.e., each momentum vector is associated with a spin locked perpendicularly to it in the surface plane. While the principal spin generation capability of topological insulators is well established, comparatively little is known about the interaction of the spins with external stimuli like polarized light. We observe a helical, bias-dependent photoconductance at the lateral edges of topological Bi2Te2Se platelets for perpendicular incidence of light. The same edges exhibit also a finite bias-dependent Kerr angle, indicative of spin accumulation induced by a transversal spin Hall effect in the bulk states of the Bi2Te2Se platelets. A symmetry analysis shows that the helical photoconductance is distinct to common longitudinal photoconductance and photocurrent phenomena, but consistent with optically injected spins being transported in the side facets of the platelets.

In-plane anisotropy of the photon-helicity induced linear Hall effect in few-layer WTe2

“…The bias-dependence clearly demonstrates that the observed V helical is not caused by a local photo-voltage generation e.g. due to builtin fields or impurities, but it is intrinsic in nature and proportional to the applied external electric field [25]. The transverse photovoltage switches polarity with the helicity of the exciting laser, which establishes that the underlying origin of the transverse conductivity is either directly based on the photon chirality [9] or on the corresponding excited spin-density in the WTe 2 [25,31,32].…”

“…The helicity independent contributions are subtracted via a fit procedure according to their characteristic frequency with the angle of the quarter-wave plate (compare supplementary Figs. S1 and S2 [20]) [25]. Line-cuts through the helical photovoltage map [ Fig.…”

Study of Surface Spin-Polarized Electron Accumulation in Topological Insulators Using Scanning Tunneling Microscopy

“…Among these properties is the ninety degree spin-momentum locking [1][2][3]8 which results in the surface accumulation of spin-polarized electrons when bias currents flow through TI samples. This spin accumulation has been studied theoretically [9][10][11][12] as well as using electrical 7,[13][14][15][16] and optical experiments 17,18 .…”

Dirac Fermion and Plasmon Dynamics in Graphene and 3D Topological Insulators

“…With respect to the spintronic application of graphene, the weak spin–orbit coupling along with the large mobility can function as a spin conserver which can transmit a spin polarization up to the spin diffusion length (>3 µm) with the spin lifetime (>0.5 ns) . On the other hand, the strong spin–orbit coupling in 3D TI promises the helical spin texture on the surface, where a spin polarization can be induced by an electric transport or the optically induced spin current . Because of the spin‐momentum locking, an oblique incidence of chiral photons can generate a transverse electric current across the transport channel, thereby 3D TI surface can be used as a spin generator in spintronic and optospintronic applications .…”