  The topological insulator Bi2Se3 shows a Raman scattering response related to
topologically protected surface states amplified by a resonant interband
transition. Most significantly this signal has a characteristic Lorentzian
lineshape and spin-helical symmetry due to collision dominated scattering of
Dirac states at the Fermi level E_F on bulk valence states. Its resonance
energy, temperature and doping dependence points to a high selectivity of this
process. Its scattering rate (Gamma=40 cm-1=5 meV) is comparable to earlier
observations, e.g. in spin-polaron systems. Although the observation of
topological surface states in Raman scattering is limited to resonance
conditions, this study represents a quite clean case which is not polluted by
symmetry forbidden contributions from the bulk

Strongly Correlated Electrons;Quantum Physics