Bulletin of the American Physical Society
APS March Meeting 2014
Volume 59, Number 1
Monday–Friday, March 3–7, 2014; Denver, Colorado
Session F42: Focus Session: Scanning Tunneling from Topological Insulators |
Hide Abstracts |
Sponsoring Units: DMP Chair: Arun Bansil, Northeastern University Room: Mile High Ballroom 4A |
Tuesday, March 4, 2014 8:00AM - 8:12AM |
F42.00001: Mapping the unconventional orbital texture in topological crystalline insulators Ilija Zeljkovic, Yoshinori Okada, Cheng-Yi Huang, R. Sankar, Daniel Walkup, Wenwen Zhou, Maksym Serbyn, Fangcheng Chou, Wei-Feng Tsai, Hsin Lin, Arun Bansil, Liang Fu, M. Zahid Hasan, Vidya Madhavan The newly discovered topological crystalline insulators (TCIs) harbor a complex band structure involving multiple Dirac cones. These materials are potentially highly tunable by external electric field, temperature or strain and could find future applications in field-effect transistors, photodetectors, and nano-mechanical systems. Theoretically, it has been predicted that different Dirac cones, offset in energy and momentum-space, might harbor vastly different orbital character, a unique property which if experimentally realized, would present an ideal platform for accomplishing new spintronic devices. In this study, we unveil the orbital texture in a prototypical TCI Pb$_{1-x}$Sn$_x$Se by using Fourier-transform (FT) scanning tunneling spectroscopy (STS) to measure the interference patterns produced by the scattering of surface state electrons. We discover that the intensity and energy dependences of FTs show distinct characteristics, which can directly be attributed to orbital effects. Our experiments also reveal the complex band topology involving two Lifshitz transitions. [Preview Abstract] |
Tuesday, March 4, 2014 8:12AM - 8:24AM |
F42.00002: Photoemission studies of topological crystalline insulator Pb$_{1-x}$Sn$_{x}$Se Ivo Pletikosic, Genda Gu, Tonica Valla Topological crystalline insulators is a class of narrow-gap semiconductors with spin-orbit induced gap inversion and surface states whose topological protection arises from the crystal symmetry.
We present a photoemission study of the electronic structure of a rock-salt alloy $Pb_{1-x}Sn_{x}Se$ that forms for $0 |
Tuesday, March 4, 2014 8:24AM - 8:36AM |
F42.00003: Spin-filtered Edge States with an Electrically Tunable Gap in a Two-Dimensional Topological Crystallin Insulator Junwei Liu, Timothy H. Hsieh, Peng Wei, Wenhui Duan, Jagadeesh Moodera, Liang Fu Three-dimensional topological crystalline insulators (TCIs) were recently predicted and observed in the SnTe class of IV-VI semiconductors, which host metallic surface states protected by crystal symmetries. In this work, we study thin films of these materials and expose their potential device applications. We demonstrate that thin films of SnTe and Pb$_{1-x}$Sn$_{x}$Se(Te) grown along the (001) direction are topologically nontrivial in a wide range of film thickness and carry conducting spin-filtered edge states that are protected by the (001) mirror symmetry via a topological invariant. Application of an electric field perpendicular to the film will break the mirror symmetry and generate a band gap in these edge states. This functionality motivates us to propose a novel topological transistor device, in which charge and spin transport are maximally entangled and simultaneously controlled by an electric field. The high on/off operation speed and coupling of spin and charge in such a device may lead to electronic and spintronic applications for TCIs. \\[4pt] [1] J. Liu, \emph{et al.}, arXiv:1310.1044 (2013), (accepted by Nature materials) [Preview Abstract] |
Tuesday, March 4, 2014 8:36AM - 9:12AM |
F42.00004: Scanning Tunneling Spectroscopy Investigations of Surface States in Three Dimensional Topological Insulators and Topological Crystalline Insulators Invited Speaker: Yoshinori Okada Three dimensional topological insulators (TIs) are a new class of material possessing topologically protected spin-polarized Dirac fermions on their surface. This new material has gathered much attention because of its great potential for realizing novel phenomena that are important for both fundamentals and applications. 3D topological insulators have been extensively probed by surface sensitive tools such as ARPES and spectroscopic imaging scanning tunneling microscopy (STM). In this talk, we will especially focus on STM measurements of Pb$_{1-x}$Sn$_{x}$Se. This material belongs to a recently discovered new category of topological insulators called topological crystalline insulators (TCIs). In TCIs, topology and crystal symmetry intertwine to create surface states with a unique set of characteristics different from conventional 3D TIs. We have discovered broken mirror symmetry driven states that coexist with massless Dirac electrons in different regions of momentum space. Our findings experimentally demonstrate the unique tunability of surface Dirac electrons which is promising for the future realization of novel electronic states within TCIs.\\[4pt] [1] Y. Okada \textit{et al}, Science \textbf{341,} 1496 (2013).\\[0pt] [2] Y. Okada \textit{et al}, Nature Commun. \textbf{3},1158 (2012).\\[0pt] [3] Y. Okada \textit{et al}, Phys. Rev. Lett. \textbf{109}, 166407 (2012).\\[0pt] [4] Y. Okada \textit{et al}, Phys. Rev. Lett. \textbf{106}, 206805 (2011). [Preview Abstract] |
Tuesday, March 4, 2014 9:12AM - 9:24AM |
F42.00005: Experimental characterization and simulation of quasi-particle-interference in the Bi-bilayer topological insulator A. Eich, M. Michiardi, G. Bihlmayer, A.A. Khajetoorians, J. Wiebe, J.-L. Mi, B.B. Iversen, Ph. Hofmann, R. Wiesendanger Topological insulators are a new class of materials with a gapless surface state where spin and momentum are locked. A Bi-bilayer is predicted to be a 2D-topological insulator and well suited for scanning probe techniques that can be utilized to probe the topological edge states. Unfortunately there are only a few substrates that allow the growth of Bismuth in the rhombohedral structure, which is essential for the formation of the bilayer. Here we present a combined experimental and theoretical study of the quasi-particle interference (QPI) in the Bi-bilayer grown on the 3D-topological insulator Bi$_2$Se$_3$. Fourier-transform-scanning-tunneling-spectroscopy reveals additional features in QPI in comparison to a bare Bi$_2$Se$_3$ surface, indicating the development of new surface states below and above the Fermi energy. Via a comparison of measured QPI-patterns and simulated QPI-patterns based on DFT calculations, the bands participating in electron scattering are identified. DFT calculations further reveal a large influence of the bilayer-substrate-distance on the resulting band structure. [Preview Abstract] |
Tuesday, March 4, 2014 9:24AM - 9:36AM |
F42.00006: Real-space imaging of Dirac-Landau orbits in Bi2Se3 Yingshuang Fu, Minoru Kawamura, Kyushiro Igarashi, Hidenori Takagi, Tetsuo Hanaguri, Takao Sasagawa Dirac wave function has two-component spinors, which is associated with pseudo-spins in graphene and real spins in the surface state of topological insulators. To date, its direct observation is still elusive. Here we demonstrate it manifests itself in the Landau orbits drifting in a Coulomb potential. We perform spectroscopic imaging scanning tunneling microscopy on the topological surface state of Bi2Se3 to reveal the energy and spatial structures of Landau orbits. Our observations are qualitatively different from those reported in a conventional massive electron system but are well reproduced by a model based on a two-component Dirac Hamiltonian. Our model further predicts energy-dependent nontrivial spin textures in a Coulomb potential, providing a unique way to manipulate spins in the topological surface state. [Preview Abstract] |
Tuesday, March 4, 2014 9:36AM - 9:48AM |
F42.00007: Identifying Antisite and Vacancy Defects in n-doped Bi$_{2}$Se$_{3}$ Topological Insulators from Scanning Tunneling Microscopy and First Principles Calculations Jeong Heum Jeon, Joon-Suh Park, Howon Kim, Won Jun Jang, Jinhee Han, Hyungjun Lee, Hyung-Joon Choi, Se-Jong Kahng Intrinsic defects are the major sources of n-type doping character in Bi$_{2}$Se$_{3}$ topological insulators, but their structural nature remains unsettled; Theoretical calculations predicted that Se$_{\mathrm{Bi}}$ antisite was the most preferred under Se-rich, i.e. molecular beam epitaxy conditions, but there has been no report on its experimental observation. Here, we present our energy-dependent atomic resolution scanning tunneling microscopy (STM) images for intrinsic defects obtained from Bi$_{2}$Se$_{3}$ thin films grown under Se-rich conditions. We observed two types of defects, and identified them as Se$_{\mathrm{Bi}}$ antisite and Bi vacancy located at Bi layer right below surface Se layer, by comparing experimental STM images with the simulated ones obtained from first principles calculations. Our study shows that, in agreement with previous predictions, not Se-vacancy at surface but Se$_{\mathrm{Bi}}$ antisite is the origin of n-type doping in our Bi$_{2}$Se$_{3}$. [Preview Abstract] |
Tuesday, March 4, 2014 9:48AM - 10:00AM |
F42.00008: Visualizing a p-n junction of two-dimensional electronic gases on a polar semiconductor BiTeI Yuhki Kohsaka, Manabu Kanou, Tetsuo Hanaguri, Hidenori Takagi, Takao Sasagawa We report atomically-resolved spectroscopic imaging studies of bipolar two-dimensional gases and their junction on the surface of a polar semiconductor BiTeI with a scanning tunneling microscope. Topographic images of pristine and substituted samples reveal that this material shows domain structures composed of opposite stacking orders, Te-Bi-I and I-Bi-Te. We find that electrons are accumulated on Te-face and holes on I-face by elaborating electronic standing waves on the surfaces of each domain, and show atomic resolution imaging of a p-n junction on the domain boundary. Given that no chemical modifications such as surface contamination and additional defects are observed, the origin of the bipolar two-dimensional carriers as well as the formation of the domain structures are ascribed to spontaneous electric polarization in the bulk. Our results indicate that, besides chemical doping and electrostatic gating, spontaneous electric polarization can induce bipolar carriers, and demonstrate a platform to study spin-split two-dimensional p-n junction and edge states at atomic resolution. [Preview Abstract] |
Tuesday, March 4, 2014 10:00AM - 10:12AM |
F42.00009: One-dimensional Topological Edge States of Bismuth Bilayers Ilya Drozdov, Aris Alexandradinata, Sangjun Jeon, Stevan Nadj-Perge, Huiwen Ji, Robert Cava, B. Andrei Bernevig, Ali Yazdani The hallmark of a time-reversal symmetry protected topologically insulating state of matter in two-dimensions (2D) is the existence of chiral edge modes propagating along the perimeter of the sample. Bilayers of bismuth (Bi), an elemental system theoretically predicted to be a Quantum Spin Hall (QSH) insulator$^{\mathrm{1}}$, has been studied with Scanning Tunneling Microscopy (STM) and the electronic structure of its bulk and edge modes has been experimentally investigated. Spectroscopic mapping with STM reveals the presence of the state bound to the edges of the Bi-bilayer. By visualizing quantum interference of the edge state quasi-particles in confined geometries we characterize their dispersion and demonstrate that their properties are consistent with the absence of backscattering. Hybridization of the edge modes to the underlying substrate will be discussed. [1] Shuichi Murakami, Phys. Rev. Lett. 97, 236805 (2006). The work at Princeton and the Princeton Nanoscale Microscopy Laboratory was supported by ARO MURI program W911NF-12-1-0461, DARPA-SPWAR Meso program N6601-11-1-4110, NSF-DMR1104612, and NSF-MRSEC programs through the Princeton Center for Complex Materials (DMR-0819860) [Preview Abstract] |
Tuesday, March 4, 2014 10:12AM - 10:24AM |
F42.00010: STM Studies of ternary topological insulators GeBi$_2$Te$_4$ and SnBi$_2$Te$_4$ Katsuya Iwaya, Tetsuo Hanaguri, Yuhki Kohsaka, Yingshuang Fu, Linda Ye, Joe Checkelsky, Yoshio Kaneko, Yoshinori Tokura We investigate topological surface states (TSSs) of three-dimensional topological insulators, GeBi$_2$Te$_4$ and SnBi$_2$Te$_4$, using low-temperature STM. Quasi-particle interference (QPI) patterns are clearly observed, as expected from the absence of back-scattering. The energy dispersions of the QPI are in good agreement with recent results from ARPES. We also find the energy of minimal local DOS, associated with the Dirac energy, spatially fluctuates due to n- and p-type atomic defects inherently existent in these intermixed systems. These results provide not only atomic-scale characterization of the defects but also a direct evidence for robust TSS against highly-disordered charged defects. [Preview Abstract] |
Tuesday, March 4, 2014 10:24AM - 10:36AM |
F42.00011: Imaging edge currents in HgTe quantum wells in the quantum spin Hall (QSH) regime Katja C. Nowack, Eric M. Spanton, Maria R. Calvo, Matthias Baenninger, Markus Koenig, Eli Fox, Andrew J. Bestwick, John R. Kirtley, Beena Kalisky, Mathias Muehlbauer, Chrsitian Ames, Philip Leubner, Christoph Bruene, Hartmut Buhmann, Laurens W. Molenkamp, David Goldhaber-Gordon, Kathryn A. Moler Conducting edge modes at the sample boundaries are a key feature of the QSH state, which was predicted and experimentally demonstrated in HgTe quantum wells. The existence of the edge modes has been inferred from conductance measurements on sufficiently small devices. Here we use a scanning SQUID to image current in devices made from HgTe quantum wells. First, I will show images of current in large Hallbars directly confirming the existence of the edge modes. Next, I will discuss progress on detecting persistent currents (PCs) flowing along the edges of anti-dots in HgTe quantum wells. The magnitude of the PC, which is periodic in flux, will depend on backscattering in the edge. Our scanning SQUID can probe currents of less than a nA, and allows us to characterize many anti-dots, one anti-dot at a time, on the same sample. The dependence of the PC on length and temperature, as well as variations between nominally identical anti-dots may provide insight into the scattering mechanisms that limit the ballistic nature of the QSH edge modes. [Preview Abstract] |
Follow Us |
Engage
Become an APS Member |
My APS
Renew Membership |
Information for |
About APSThe American Physical Society (APS) is a non-profit membership organization working to advance the knowledge of physics. |
© 2024 American Physical Society
| All rights reserved | Terms of Use
| Contact Us
Headquarters
1 Physics Ellipse, College Park, MD 20740-3844
(301) 209-3200
Editorial Office
100 Motor Pkwy, Suite 110, Hauppauge, NY 11788
(631) 591-4000
Office of Public Affairs
529 14th St NW, Suite 1050, Washington, D.C. 20045-2001
(202) 662-8700