Bulletin of the American Physical Society
APS March Meeting 2014
Volume 59, Number 1
Monday–Friday, March 3–7, 2014; Denver, Colorado
Session M42: Spectroscopy of Topological Insulators |
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Sponsoring Units: DCMP Chair: Andrei Sushkov, University of Maryland Room: Mile High Ballroom 4A |
Wednesday, March 5, 2014 11:15AM - 11:27AM |
M42.00001: Appearance and suppression of electron interference patterns on the surface of Ho$_{0.05}$Bi$_{1.95}$Se$_{3}$ Hyeokshin Kwon, Wonhee Ko, Insu Jeon, Hyo Won Kim, JiYeon Ku, Youngtek Oh, Paul Syers, Johnpierre Paglione, Sung Woo Hwang, Hwansoo Suh We present study on the surface property of a magnetically doped topological insulator, Ho$_{0.05}$Bi$_{1.95}$Se$_{3}$. By using scanning tunneling microscopy (STM) and spectroscopy (STS), we obtained topographic images with several distinct types of defects, some of which originate from Holmium dopant atoms and conductance maps at various bias voltages. It is found that conductance maps in the upper and lower branches of helical Dirac cone show interference patterns around the defects. Interestingly, the interference patterns were substantially suppressed in the range of 40 meV close to the Dirac point. Our analysis shows that the surface states of Ho$_{0.05}$Bi$_{1.95}$Se$_{3}$ behave differently than other magnetically doped topological insulators. [Preview Abstract] |
Wednesday, March 5, 2014 11:27AM - 11:39AM |
M42.00002: Quasiparticle interference on the surfaces of the of the layered topological superlattice Bi$_{4}$Se$_{3}$ Daniel Walkup, Ilija Zeljkovic, Hsin Lin, Wenwen Zhou, Madhab Neupane, Raman Sankar, Kane Scipioni, Arun Bansil, Fangcheng Chou, M. Zahid Hasan, Vidya Madhavan Three-dimensional topological insulators (TIs) host robust surface states with massless Dirac-like dispersion and helical spin texture. The possibility of layering TIs with other materials in a superlattice is especially intriguing, as exotic phenomena are predicted to occur at their boundary. Here, we present scanning tunneling microscopy and spectroscopy (STM/STS) results on one of the simplest such superlattices, Bi$_{4}$Se$_{3}$, which consists of alternating layers of a three-dimensional TI, Bi$_{2}$Se$_{3}$, and a two-dimensional TI, Bi$_{2}$. STM topographs reveal two distinct, alternating surfaces, each of which harbors dispersing surface states. By using Fourier-transform STS, we characterize the dispersion of these states, which is considerably more complex than that of the single Dirac cone found in prototypical three-dimensional TIs. In addition, we show that the surface states of Bi$_{4}$Se$_{3}$ are strongly influenced by proximity to atomic defects. [Preview Abstract] |
Wednesday, March 5, 2014 11:39AM - 11:51AM |
M42.00003: Evolution of Topological Surface States in Tunable Topological Insulators Guanggeng Yao, Ziyu Luo, Wentao Xu, Yuanping Feng, Xue-sen Wang Bi$_{\mathrm{1-x}}$Sb$_{x}$ (0.07\textless $x$\textless 0.22) is the first generation of 3D topological insulators (TIs), possessing a bandgap and topological surface states (SSs) generated by spin-orbit coupling In fact, within the whole range of 0\textless $x$\textless 1 (i.e. from pure Bi to pure Sb), a topological phase transition has to occur as the system is twisted from topologically trivial to nontrivial phases, even though it becomes a semimetal hosting a negative indirect gap Therefore, taking advantage of Fourier-transform scanning tunneling spectroscopy (FT-STS) and \textit{ab initio} calculations, we investigate the progressive evolution of topological SSs in the tunable Bi$_{\mathrm{1-x}}$Sb$_{x}$ (0\textless $x$\textless 1) materials grown by means of molecular beam epitaxy In alloys with several representative compositions, quasiparticle interference (QPI) patterns of SSs exhibit dramatic dependence on $x$ values, indicating that intra-surface scatterings are ultimately determined by band structures and the associated spin textures. Additionally, the corresponding simulated QPI patterns are also revealed based on \textit{ab initio} calculations. Such systematic studies of the Bi$_{\mathrm{1-x}}$Sb$_{x}$ alloy family can be further explored to tailor surface energetic and transport properties for potential applications in quantum information, spintronics and many other topological quantum phenomena. [Preview Abstract] |
Wednesday, March 5, 2014 11:51AM - 12:03PM |
M42.00004: Scanning tunneling spectroscopic (STS) studies of the bulk magnetic doping effects on the surface state of Bi$_{2}$Se$_{3}^{\ast }$ C.-C. Chen, M.L. Teague, N.D. Woodward, N.-C. Yeh, L. He, X. Kou, M. Lang, K.-L. Wang We report STS studies of MBE-grown undoped and Cr-doped Bi$_{2}$Se$_{3}$ bi-layers on InP (111) and as a function of the updoped layer thickness and the Cr-doping level ($x)$. Our studies reveal \textit{gapless} Dirac spectra at all temperatures ($T)$ for samples with an undoped top layer larger than 5 QLs, implying that the interlayer magnetic correlation length $\xi_{\bot }$ is \textless $\sim$ 5-QL. For samples with an undoped top layer smaller than 5 QLs, STS reveals \textit{gapped} spectra at $T$ \textless $T_{c}=$ (260 $\pm$ 20) K. The gap is spatially inhomogeneous and increases with decreasing $T$, reaching an $x$-independent maximum $\Delta =$ (0.8 $\pm$ 0.2) eV at $T$ \textless \textless $T_{c}$. Further, the gap inhomogeneity increases with decreasing $x$, showing magnetic clusters separated by gapless regions and an in-plane magnetic correlation length $\xi_{\vert \vert }$ $\sim$ 8-QL. We also find spatially localized double and single resonance peaks in the gapless regions, and their areal densities peak near $T_{c}$. We attribute the resonance sites to isolated Cr impurities, which couple with the spins of surrounding Dirac electrons and form localized topological spin textures of a long lifetime. With increasing interlayer magnetic field, the resonance sites diminish and the gap distribution becomes more homogeneous. [Preview Abstract] |
Wednesday, March 5, 2014 12:03PM - 12:15PM |
M42.00005: Anisotropic Dirac Cones in SrMnBi2 and CaMnBi2 Revealed by Angle-Resolved Photoemission Ya Feng, Chaoyu chen, Youguo Shi, Zhuojin Xie, Hemian Yi, Aiji Liang, Shaolong He, Junfeng He, Yingying Peng, Xu Liu, Yan Liu, Lin Zhao, Guodong Liu, Xiaoli Dong, Jun Zhang, Li Yu, Chuangtian Chen, Zuyan Xu, Xingjiang Zhou By carrying out high resolution angle-resolved photoemission measurements on SrMnBi2 and CaMnBi2, we have directly revealed the existence of anisotropic Dirac cone in these two compounds. In particular, we find that SrMnBi2 and CaMnBi2 exhibit markedly different anisotropy in their Dirac cone. In SrMnBi2, four Dirac cones are well separated in the first Brillouin zone forming four crescent moon-like Fermi surface sheets and the ratio of Fermi velocities along and perpendicular to Gamma-M direction is $\sim$18. In CaMnBi2, however, the Dirac cones are connected in the first Brillouin zone forming a ridge-like Fermi surface topology indicating CaMnBi2 as a new Dirac material with a single Dirac cone and giant Dirac anisotropy. The dichotomy of the Dirac cone anisotropy between SrMnBi2 and CaMnBi2 originates from a different local Sr (Ca) arrangement surrounding the Bi square net. It demonstrates the feasibility in engineering the Dirac cone anisotropy by manipulating the environment of the Bi square net. [Preview Abstract] |
Wednesday, March 5, 2014 12:15PM - 12:27PM |
M42.00006: ABSTRACT WITHDRAWN |
Wednesday, March 5, 2014 12:27PM - 12:39PM |
M42.00007: Probing the pressure-induced topological phase transition in BiTeI Xiaoxiang Xi, Chunli Ma, Zhenxian Liu, Zhiqian Chen, Wei Ku, H. Berger, C. Martin, D.B. Tanner, G.L. Carr The recent intensive development of topological insulators was boosted by the discovery of real material systems. To expand the topological insulator family, pressure has been proposed to induce topological phase transitions in a variety of topologically trivial materials, but experimental realization is hindered by the lack of appropriate surface-sensitive probes applicable under high pressure. Here we discuss signatures of pressure-induced band gap closing and reopening in the bulk of the narrow-gap semiconductor BiTeI from infrared spectroscopy and x-ray powder diffraction. Combined with theoretical calculations, our experimental results strongly support a pressure-induced topological phase transition in BiTeI. These experimental methods can be valuable in the study of certain topological phase transitions when surface-sensitive probes are not applicable. [Preview Abstract] |
Wednesday, March 5, 2014 12:39PM - 12:51PM |
M42.00008: Infrared Magnetospectroscopy of Dirac Plasmons in Topological Insulator Ribbons Yuxuan Jiang, Wenlong Yu, Jean-Marie Poumirol, Matthew Brahlek, Nikesh Koirala, Seongshik Oh, Wei Pan, Dmitry Smirnov, Zhigang Jiang We present the infrared spectroscopy study of magnetoplasmons in patterned topological insulator (Bi$_{2}$Se$_{3})$ ribbon arrays. The measurement is performed in Faraday configuration with incident infrared light polarized parallel or perpendicular to the ribbon direction and in a high magnetic field up to 18 T. We demonstrate that the collective oscillations of Dirac fermions (i.e., plasmons) in topological insulators can be coupled with the cyclotron resonance, forming the so-called upper-hybrid-mode. This mode exhibits a characteristic magnetic field dependence, with an effective mass consistent with that obtained from the unpatterned two-dimensional sample. Due to the high quality of the MBE grown topological insulator thin films, a higher order plasmon mode is also evidenced in our measurements. This work is supported by the DOE (DE-FG02-07ER46451), the NSF (DMR-0845464), and the ONR (N000141210456). [Preview Abstract] |
Wednesday, March 5, 2014 12:51PM - 1:03PM |
M42.00009: Optical properties of the doped Bi$_{2}$Te$_{3}$ single crystals: electron-phonon coupling and bulk-boundary correspondence Byung Cheol Park, N.H. Cho, K.J. Lee, M.H. Jung, Jae Hoon Kim We studied the optical properties of Bi$_{2}$Te$_{3}$ single crystals doped with La (8{\%}), Ce (8{\%}), Fe(8{\%}, 15{\%}) via a combination of terahertz time-domain spectroscopy and spectroscopic ellipsometry. We observed the Drude peak and the in-plane phonon near 60 cm$^{-1}$ in the optical conductivity in the terahertz regime as well as the absorptions corresponding to the bulk interband transitions in the far-infrared and the visible-ultraviolet regions. We confirmed that the terahertz in-plane phonon asymmetry can be employed as spectroscopic evidence in order to investigate the electron-phonon interaction arising from external dopants while the bulk band structure can be determined from ellipsometry. [Preview Abstract] |
Wednesday, March 5, 2014 1:03PM - 1:15PM |
M42.00010: Raman Scattering studies of Topological Insulators Bi$_2$Te$_3$, Bi$_2$Se$_3$, and Sb$_2$Te$_3$ Kolawole Akintola, Todd Andrews, Stephanie Curnoe, Takao Sasagawa Raman scattering spectroscopy has been used to probe the bismuth and antimony chalcogenides Bi$_2$Se$_3$, Bi$_2$Te$_3$, and Sb$_2$Te$_3$. Room temperature spectra of these topological insulators reveal new phonon modes in spectral regions not previously investigated. Polarization studies have been done to characterize these modes. New results on the temperature dependence of the Raman active phonon modes in these materials will also be presented. [Preview Abstract] |
Wednesday, March 5, 2014 1:15PM - 1:27PM |
M42.00011: Optics of midgap impurity states on a surface of a topological insulator Justin Wilson, Dmitry Efimkin, Victor Galitski The time reversal symmetry breaking on a surface of a topological insulator leads to a pronounced anomalous quantum Hall effect that can manifest itself in the quantized Kerr and Faraday effects [1,2]. The symmetry can be broken by magnetic impurities introduced to the TI bulk which tend to order and to gap the surface spectrum. We investigate the role of midgap impurity states in the surface spectrum in optics, particularly in the Faraday and Kerr effects. 1. J. Maciejko, X.L. Qi, H.D. Drew, S.C. Zhang, Phys. Rev. Lett., 105, 166803 (2010). 2. W.-K. Tse and A. H. MacDonald, Phys. Rev. B 82, 161104 (2010). [Preview Abstract] |
Wednesday, March 5, 2014 1:27PM - 1:39PM |
M42.00012: Spectroscopic Evidence for the Emergence of a Half-Metallic Surface State on the Bulk Insulator Sodium Cobaltate Alex W. Contryman, Francis Niestemski, Gang Xu, Haijun Zhang, Sukbum Chung, Yulin Chen, Thorsten Hesjedal, Shreyas G. Patankar, Daniel Golubchik, Joseph Orenstein, Z.X. Shen, Shoucheng Zhang, Hari C. Manoharan In recent years Na$_{x}$CoO$_{2}$ has attracted much attention for its unconventional superconductivity and antiferromagnetic phases. More recently, the stoichiometric compound NaCoO$_{2}$ has been proposed as a platform for achieving topological superconductivity through its predicted half-metallic surface state. We characterize this surface state and its relationship to local sodium concentration using low-temperature scanning tunneling spectroscopy (STS) and tuning fork-based atomic force microscopy. We also examine the magnetic moment of the surface state through temperature-dependent STS and Kerr rotation spectroscopy. These results are compared with density functional theory-calculated band structure and local density of states. [Preview Abstract] |
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