Impurity-induced states on the surface of three-dimensional topological insulators

Abstract

We calculate the modification of the local electronic structure caused by a single local impurity on the surface of a 3D Topological Insulator. We find that the LDOS around the Dirac point of the electronic spectrum at the surface is significantly disrupted near the impurity by the creation of low-energy resonance state(s) -however, this is not sufficient to (locally) destroy the Dirac point. We also calculate the non-trivial spin textures created near the magnetic impurities and discover anisotropic RKKY coupling between them. PACS numbers: 72.25.Dc, 75.30.Hx,d * Electronic address: rrbiswas@physics.harvard.edu † Electronic address: avb@lanl.gov 1 A. V. Balatsky, I. Vekhter, and J.-X. Zhu, Rev. Mod. Phys. 78, 373 (2006).

Strong potential impurities on the surface of a topological insulator

“…Theoretical results for non-magnetic impurities using a continuum model for the Dirac surface state have indeed shown on both absence of backscattering 4 , as also confirmed experimentally, 5 and how these impurities never destroy, even locally, the low-energy spectrum, including the Dirac point. 6 This is in contrast to magnetic impurities, which have theoretically been shown to open a gap in the surface spectrum. 7 Taken together, these results make TIs intriguing candidates for both spintronic devices and topological quantum computation.…”

“…Thus, for the dilute impurity case n → ∞, we expect a single resonance peak to be present in the low-energy spectrum, contrary to 2D surface state continuum model results. 6 We attribute this difference to the 3D dimensionality of the problem. In Fig.…”

In-Plane Magnetic Anisotropy of Fe Atoms onBi2Se3(111)

“…It has been suggested that the interaction between magnetic impurities and the topological state can cause an opening of an energy gap at the Dirac point (DP), provided that the magnetic order is oriented normal to the surface plane [5][6][7]. Nevertheless, the stability of the TSS against local magnetic perturbations is currently under heavy debate [8][9][10], since little is known about the fundamental interface effects of magnetic entities with TI surfaces as well as the static magnetic properties of impurities in these materials.In this work we present a comprehensive study of the magnetic properties of iron impurities on a prototypical TI Bi 2 Se 3 using local scanning tunneling microscopy (STM) and integral x-ray magnetic circular dichroism (XMCD) techniques. We show that the multiplet structure visible in x-ray absorption spectra reflect a high-spin state of the adsorbed Fe impurities, which are confirmed to bind at hollow sites of the surface lattice, under the influence of trigonal crystal fields given in hollow site positions of the Bi 2 Se 3 surface.…”

“…It has been suggested that the interaction between magnetic impurities and the topological state can cause an opening of an energy gap at the Dirac point (DP), provided that the magnetic order is oriented normal to the surface plane [5][6][7]. Nevertheless, the stability of the TSS against local magnetic perturbations is currently under heavy debate [8][9][10], since little is known about the fundamental interface effects of magnetic entities with TI surfaces as well as the static magnetic properties of impurities in these materials.…”

Spin-polarized states of matter on the surface of a three-dimensional topological insulator with implanted magnetic atoms

“…If the chemical potential μ is finely tuned at the conical point of the spectrum of the SS, the effective interaction between two local moments at a distance r apart monotonically decays as r −3 and the magnetic phase diagram (Curie temperature versus concentration of magnetic moments) can be qualitatively obtained within a mean-field approach. 5 However, when μ falls within the band, a serious problem arises to identify the FM region in the phase diagram, 6 due to the appearance of an oscillating contribution to the interaction with slowly varying amplitude 7 (∼r −2 ) that makes the mean-field approach problematic. Recently, 8 a description was proposed, which treats the local moments at a mean-field level, in the case when these are localized in deep levels, but cannot describe the situation when the TM atoms form shallow levels near the conical point of the spectrum and are rather delocalized.…”