  The massless Dirac electrons found at topological insulator surfaces are
thought to be influenced very little by weak, non-magnetic disorder. However, a
resonance effect of strongly perturbing non-magnetic impurities has been
theoretically predicted to change the dispersion and physical nature of
low-energy quasiparticles, resulting in unique particle-like states that lack
microscopic translational symmetry. Here we report the direct observation of
impurities reshaping the surface Dirac cone of the model 3D topological
insulator Bi2Se3. For the first time, a pronounced kink-like dispersion feature
is observed in disorder-enriched samples, and found to be closely associated
with the anomaly caused by impurity resonance in the surface state density of
states, as observed by dichroic angle resolved photoemission spectroscopy
(ARPES). The experimental observation of these features, which closely resemble
theoretical predictions, has significant implications for the properties of
topological Dirac cones in applied scenarios that commonly feature point defect
disorder at surfaces or interfaces.
