Abstract
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.
Highlights
Crystallographic point defects occur in typical bulk-grown Bi2Se3 samples with relatively low densities of ~
(LD-ARPES) investigation of defect-enriched Bi2Se3, and report the experimental observation of a topological surface Dirac cone indicate that the resulting Bi2Se3 samples realize a large density of point defects while maintaining good single-phase crystallinity
Surface doping of Bi2Se3 by adatoms and photon exposure is a natural concern in quantitative ARPES experiments, and multiple doping mechanisms can come into play.[19,33,39,40,41,42,43,44,45,46,47]
Summary
Three-dimensional topological insulators are bulk semiconductors with spin-helical Dirac cone surface states that span the bulk band gap.[1,2] Since their discovery around 2007,3–6 the topological Dirac cone has appeared at the heart of a wide range of proposals for novel emergent quasiparticles and next-generation electronics, such as for the realization of exotic dyon-based, axion-based, or Majorana fermion-based physics.[1,2,7,8,9,10] the spin-helical Dirac surface states are very robust against dilute non-magnetic impurities due to intrinsic immunities to backscattering and Anderson localization,[11,12,13,14,15,16] and numerous studies have shown the surface Dirac cone remains qualitatively intact in the presence of weak non-magnetic disorder.[17,18,19] local probe studies have found that the effect of disorder on the real space electronic structure can be remarkably strong. The resistance of topological surface electrons to Anderson localization and backscattering is thought to result in a unique quasiparticle-like character for electrons at the impurity resonance Though these electrons profoundly lack translational symmetry, simulations suggest that their width cross-section in momentum space is narrower than one inverse wavelength,[28,29] and meets the nominal definition for a “good” quasiparticle. This is quite surprising, and means that inducing disorder at a topological insulator surface may enable the first experimental realization of. The larger scale morphology of such highly disordered samples has been problematic for high-
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