Lawrence Berkeley National Laboratory

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 three-dimensional topological insulator bismuth selenide. 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. 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. Topological insulators - influence of surface impurities: The electronic properties of topological insulators are robust against perturbations, including the presence of non-magnetic impurities. However, surface impurities can give rise to resonant states near the Dirac point, and if their density becomes sufficiently high it is predicted that they can substantially modify the dispersion of the Dirac cone and develop a collective behaviour that results in the formation of particle-like states that lack microscopic translational symmetry. L. Andrew Wray at Purdue University and at the New York University Shanghai, and colleagues, used angle-resolved photoemission spectroscopy to experimentally observe the reshaping of the surface Dirac cone in a defect-rich sample of the topological insulator Bi2Se3. These results indicate that surface impurities can provide a useful handle to control the properties of topological insulators.