  Topological insulators represent a new quantum state of matter that are
insulating in the bulk but metallic on the edge or surface. In the Dirac
surface state, it is well-established that the electron spin is locked with the
crystal momentum. Here we report a new phenomenon of the spin texture locking
with the orbital texture in a topological insulator Bi2Se3. We observe
light-polarization-dependent spin texture of both the upper and lower Dirac
cones that constitutes strong evidence of the orbital-dependent spin texture in
Bi2Se3. The different spin texture detected in variable polarization geometry
is the manifestation of the spin-orbital texture in the initial state combined
with the photoemission matrix element effects. Our observations provide a new
orbital degree of freedom and a new way of light manipulation in controlling
the spin structure of the topological insulators that are important for their
future applications in spin-related technologies.
