  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
the accumulated spins being transported in the side facets of the platelets.
Our findings demonstrate that spin effects in the facets of 3D topological
insulators can be addressed and read-out in optoelectronic devices even at room
temperatures.
