  We report high-resolution spin-resolved photoemission spectroscopy
(Spin-ARPES) measurements on the parent compound Sb of the recently discovered
3D topological insulator Bi1-xSbx [D. Hsieh et al., Nature 452, 970 (2008)]. By
modulating the incident photon energy, we are able to map both the bulk and
(111) surface band structure, from which we directly demonstrate that the
surface bands are spin polarized by the spin-orbit interaction and connect the
bulk valence and conduction bands in a topologically non-trivial way. A unique
asymmetric Dirac surface state gives rise to a k-splitting of its spin
polarized electronic channels. These results complement our previously
published works on this materials class and re-confirm our discovery of
topological insulator states in the Bi-Sb series.
