Bulletin of the American Physical Society
APS March Meeting 2011
Volume 56, Number 1
Monday–Friday, March 21–25, 2011; Dallas, Texas
Session D2: Topological Surface States |
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Sponsoring Units: DCMP Chair: Ali Yazdani, Princeton University Room: Ballroom A2 |
Monday, March 21, 2011 2:30PM - 3:06PM |
D2.00001: Visualizing surface states of topological insulators using spectroscopic mapping with the scanning tunneling microscope Invited Speaker: In topological insulators, the spin texture of the surface states makes them distinct from conventional two-dimensional electron states, and leads to novel properties for these states. These surface states are expected to be immune to localization and to overcome barriers caused by material imperfections. We have used scanning tunneling microscopy and spectroscopy to study the topological surface states in \textit{Bi}$_{0.9}$\textit{Sb}$_{0.1}$\textit{, Sb, } and \textit{Bi}$_{2}$\textit{Te}$_{3}$. By mapping the interference of the surface states scattering off random alloying disorder in \textit{Bi}$_{0.9}$\textit{Sb}$_{0.1}$, we have demonstrated that despite strong atomic scale disorder, backscattering between states of opposite momentum and opposite spin is absent, resulting from the spin texture [1]. Furthermore, we have measured the transmission and reflection of topological surface states of \textit{Sb} through atomic terraces [2]. In contrast to Schottky surface states of noble metals, these surface states penetrate such barriers with high probability. To examine the possibility of disorder induced localization, we investigated the surface states of Bi$_{2}$Te$_{3}$ in the presence of local defects. In the presence of magnetic dopants, we have observed an interference pattern throughout a broad range of energies, even in the region of linear dispersion near the Dirac point [3]. We discuss the results of a statistical analysis of these patterns which can help to learn about the tendency toward localization for these surface states and how this trend is affected as the energy is tuned to the Dirac point. *Work was done in collaboration with J. Seo, H. Beidenkopf, L. Gorman, Y. S. Hor, C. Parker, D. Hsieh, and A. Richardella, M. Z. Hasan, R. Cava, and A. Yazdani. \\[4pt] [1] P. Roushan \textit{et al.} Nature 460, 1106 (2009). \\[0pt] [2] J. Seo \textit{et al.} Nature 466, 343 (2010). \\[0pt] [3] H. Beidenkopf \textit{et al.} (2010). [Preview Abstract] |
Monday, March 21, 2011 3:06PM - 3:42PM |
D2.00002: STM and STS studies of electronic states near macroscopic defects in topological insulators Invited Speaker: Bi$_{2}$Te$_{3~}$and Bi$_{2}$Se$_{3~}$have been argued recently to be three-dimensional (3D) topological insulators (TI), exhibiting a bulk gap and a single, non-degenerate Dirac fermion surface band topologically protected by time-reversal symmetry. In this talk we will discuss the physics of topological insulators. We will show that Scanning tunneling spectroscopy (STS) studies on high-quality Bi$_{2}$Te$_{3}$~and Bi$_{2}$Se$_{3}$~crystals exhibit perfect correspondence to ARPES data, hence enabling identification of different regimes measured in the local density of states (LDOS). Unique to Bi$_{2}$Te$_{3}$, we will discuss observations of oscillations of LDOS near a step. Within the main part of the surface band we found that the oscillations are strongly damped, supporting the hypothesis of topological protection. At higher energies, as the surface band becomes concave, oscillations appear which disperse with a particular wave-vector that results from an unconventional hexagonal warping term in the surface-state-band Hamiltonian [1]. For both systems, a bound state was observed in the bulk gap region that runs parallel to the edge of the defect and is bound to it at some characteristic distance. An expression that fits the data, and provides further insight into the general topological properties of the electronic structure of the surface band near strong structural defects, can be obtained using the full three-dimensional Hamiltonian of the system. \\[4pt] [1] Zhanybek Alpichshev, J. G. Analytis, J.-H. Chu, I. R. Fisher, Y. L. Chen, Z. X. Shen, A. Fang, and A. Kapitulnik \textit{Phys. Rev. Lett.} \textbf{104} 016401 (2010) [Preview Abstract] |
Monday, March 21, 2011 3:42PM - 4:18PM |
D2.00003: Theory of Topological Insulators and Superconductors: Application to Cux-Bi2Se3 Invited Speaker: This abstract not available. [Preview Abstract] |
Monday, March 21, 2011 4:18PM - 4:54PM |
D2.00004: Investigation and manipulation of the electronic properties of magnetically doped topological insulators Invited Speaker: Topological insulator (TI) is characterized by gapless surface/edge states which are protected by time reversal symmetry (TRS). Magnetic order in or adjacent to a TI can break its TRS, and thus result in various exotic phenomena, e.g. magnetic monopole, quantum anomalous Hall effect, and topological magneto-electric effect. Combining angle-resolved photoemission spectroscopy, scanning tunneling microscopy/spectroscopy, and transport measurement, we have investigated the electronic structures and properties of Bi2Se3 family three dimensional TIs doped with magnetic impurities. Gap opening at the Dirac surface states induced by magnetic impurities has been observed, suggesting the formation of long range magnetic order in the TIs. The Dependences of the gap size on impurity concentration, chemical potential and real space position and the (anomalous) Hall effect of the magnetically doped TIs have been systematically studied, the result of which reveals the nature and mechanism of the magnetic order. The present studies pave the road to the realization of the novel properties predicted in magnet/TI heterostructures. [Preview Abstract] |
Monday, March 21, 2011 4:54PM - 5:30PM |
D2.00005: Theory of surface phenomena in topological insulators Invited Speaker: Recently discovered topological insulators (TIs) are materials with bulk bandgap and robust gapless surface states protected by topological invariants that characterize their bulk band structure. After a brief introduction to the physics of TIs I will describe recent theoretical advances in understanding the behavior of surface electrons in the presence of both magnetic and non-magnetic impurities, surface steps, as well as magnetic and superconducting coating. The key property of the topological surface states -- absence of backscattering from non-magnetic defects -- leads to a number of features that stand in a stark contrast to the physics of ordinary non-topological states. Among these are vastly enhanced transmission through crystal steps, absence of quasiparticle interference patterns caused by non-magnetic impurities and formation of a gap in the presence of magnetic impurities. [Preview Abstract] |
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