  When electrons are subject to a large external magnetic field, the
conventional charge quantum Hall effect \cite{Klitzing,Tsui} dictates that an
electronic excitation gap is generated in the sample bulk, but metallic
conduction is permitted at the boundary. Recent theoretical models suggest that
certain bulk insulators with large spin-orbit interactions may also naturally
support conducting topological boundary states in the extreme quantum limit,
which opens up the possibility for studying unusual quantum Hall-like phenomena
in zero external magnetic fields. Bulk Bi{1-x}Sbx single crystals are predicted
to be prime candidates for one such unusual Hall phase of matter known as the
topological insulator. The hallmark of a topological insulator is the existence
of metallic spin-textured surface states that are higher dimensional analogues
of the edge states that characterize a quantum spin Hall insulator. Here, using
incident-photon-energy-modulated angle-resolved photoemission spectroscopy, we
report the direct observation of massive Dirac particles in the bulk of
Bi0.9Sb0.1, locate the Kramers' points at the sample's boundary and provide a
comprehensive mapping of the topological Dirac insulator's gapless surface
modes. These findings taken together suggest that the observed surface state on
the boundary of the bulk insulator is a realization of the much sought exotic
"topological metal". They also suggest that this material has potential
application in developing next-generation quantum computing devices that may
incorporate "light-like" bulk carriers and topologically protected
spin-textured edge-surface currents. This work is a detailed version of [Hsieh
et.al., NATURE 452, 970 (2008), {Submitted in November 2007}].
