Bulletin of the American Physical Society
APS March Meeting 2017
Volume 62, Number 4
Monday–Friday, March 13–17, 2017; New Orleans, Louisiana
Session Y8: Topological Insulators (Spectroscopy) |
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Sponsoring Units: DCMP Room: 267 |
Friday, March 17, 2017 11:15AM - 11:27AM |
Y8.00001: Quantum oscillations from Fermi sea Hridis Pal Quantum oscillations are conventionally understood to arise from the Fermi level; hence, they are considered to be a proof of the existence of an underlying Fermi surface. Here, I show that in certain situations quantum oscillations can also arise from inside the Fermi sea. The necessary condition and possible scenarios for such unusual behavior will be pointed out. In particular, in strongly particle-hole asymmetric insulators, models of which have been recently used in the context of the topological Kondo insulator SmB$_6$, I show that oscillations have no connection with the gap, but arise from inside the filled band. [Preview Abstract] |
Friday, March 17, 2017 11:27AM - 11:39AM |
Y8.00002: Shift charge and spin photocurrents in Dirac surface states of topological insulator Kun Woo Kim, Takahiro Morimoto, Naoto Nagaosa The generation of photocurrent in condensed matter is of main interest for photovoltaic and opto-electronic applications. Shift current, a nonlinear photoresponse, has attracted recent intensive attention as a dominant player of bulk photovoltaic effect in ferroelectric materials. In three-dimensional topological insulators Bi$_{\mathrm{2}}$X$_{\mathrm{3}}$ (X: Te, Se), we find that Dirac surface states with a hexagonal warping term support shift current by linearly polarized light. Moreover, we study ``shift spin current'' that arises in Dirac surface states by introducing time-reversal symmetry breaking perturbation. The estimate for the magnitudes of the shift charge and spin current densities are 0.13 I$_{\mathrm{0}}$ and 0.40 I$_{\mathrm{0\thinspace }}$(nA/m) for Bi$_{\mathrm{2}}$Te$_{\mathrm{3}}$ with the intensity of light I$_{\mathrm{0}}$ measured in (W/m$^{\mathrm{2}})$, respectively, which can offer a useful method to generate these currents efficiently. [Preview Abstract] |
Friday, March 17, 2017 11:39AM - 11:51AM |
Y8.00003: Extracting current induced spins from topological insulator wires: gate control of extracted spin polarization Inanc Adagideli Spin-momentum locking featured by the surface states of 3D topological insulators (TIs) allows electrical generation of spin accumulations and provides a new avenue for spintronics applications. In this work [1], we explore how to extract electrically induced spins from topological insulator surfaces, where they are generated into topologically trivial metallic leads that are commonly used in conventional electronic devices. We first focus on an effective surface theory of current induced spin accumulation in topological insulators. Then we focus on a particular geometry: a metallic pocket attached to top and side faces of a 3D topological insulator quantum wire with a rectangular cross section, and explore spin extraction into topologically non-trivial materials. We find surprisingly that the doping in and/or a gate voltage applied to the metallic side pocket can control the direction of the extracted spin polarization opening the possibility for a spin transistor operation of these device geometries. We also perform numerical simulations of nonequilibrium spin accumulations generated by an applied bias in the same geometry and demonstrate the spin polarization control via applied gate voltages. [1] A. Asgharpour, C. Gorini, K.Richter, I. Adagideli [Preview Abstract] |
Friday, March 17, 2017 11:51AM - 12:03PM |
Y8.00004: Raman study of lattice instability in non-symmorphic topologica linsulator KHgSb D. Chen, T.-T. Zhang, C.-J Yi, T. Zhang, Y.-G Shi, H.-M. Weng, Z. Fang, P. Richard, H. Ding, W.-L. Zhang In previously discovered topological insulators, edge or surface states appear as Dirac cones protected by time-reversal symmetry or symmorphic crystalline symmetry. As a new class of topological states, hourglass-like electronic surface states protected by non-symmorphic glide mirror symmetry have been predicted recently in KHgSb [1] and their existence supported by ARPES experiments [2]. In spite of a clear description of its electronic structure, the lattice dynamics of KHgSb, which plays an important role here, is unknown. In this work, we report the first polarized Raman scattering study of KHgSb. Our results suggest a lattice instability below $T^*$ = 150 K. Accompanied with this structure instability, two-phonon excitations are enhanced. We also discuss the decomposition of the samples at high temperature and under high laser power. [1] Z. Wang \emph{et al.}, Nature \textbf{532}, 189 (2016) [2] J.-Z. Ma \emph{et al.}, Arxiv: 1605.06824 (2016) [Preview Abstract] |
Friday, March 17, 2017 12:03PM - 12:15PM |
Y8.00005: A local characterization of the insulating state Raffaele Resta, Antimo Marrazzo An insulator differs from a metal because of a different organization of the electrons in their ground state. This feature can be probed by means of the quantum metric tensor: a geometrical property, inspired by---and closely related to---the modern theory of polarization. Such tensor addresses the system as a whole, and it is therefore limited to macroscopically homogeneous samples. Here we show that the same approach leads to a local marker, which can detect the metallic vs. insulating character of a given sample region using as sole ingredient the ground state many-body wavefunction. Simulations on paradigmatic systems validate our theory. [Preview Abstract] |
Friday, March 17, 2017 12:15PM - 12:27PM |
Y8.00006: Observation of an unconventional collective mode on the surface of a topological insulator Xuetao Zhu, Xun Jia, Shuyuan Zhang, Raman Sankar, Fang-Cheng Chou, E.W. Plummer, Jiandi Zhang, Jiandong Guo Using a high resolution electron energy loss spectroscopy (HREELS) system with the function of two-dimensional energy and momentum mapping, we studied the surface collective modes of a prototypical three-dimensional topological insulator Bi$_{\mathrm{2}}$Se$_{\mathrm{3}}$ with Dirac surface state, and observed a new surface collective mode with energy dispersing from 0 to 10 meV. In contrast, on the surface of Mn-doped Bi$_{\mathrm{2}}$Se$_{\mathrm{3}}$, the mode does not exist due to the absence of the Dirac surface state because of magnetic doping. Thus we conclude the observed low energy collective mode is originated from the surface Dirac electrons. This new HREELS system allows us to detect the collective modes in a large momentum range up to the second Brillouin zone center of Bi$_{\mathrm{2}}$Se$_{\mathrm{3}}$. Unlike the plasmons from regular conducting electrons, which decay into incoherent electron-hole excitations (Landau damping) when entering the electron-hole pair continuum, and disappear at large momentum, this new mode remains prominent in a large momentum range far beyond the electron-hole pair continuum. [Preview Abstract] |
Friday, March 17, 2017 12:27PM - 12:39PM |
Y8.00007: Electron-beam nanosculpting and materials analysis of exfoliated bismuth selenide Sarah Friedensen, William Parkin, Jerome Mlack, Marija Drndic We report on nanosculpting Bi$_2$Se$_3$ with a highly-focused electron beam in a scanning transmission electron microscope (STEM). Exfoliated Bi$_2$Se$_3$ flakes were transferred onto silicon nitride TEM windows and structures at least 100 nm by 100 nm in size were selected for shaping. Focused ion beam (FIB) cutting was used to carve larger features into the structures and provide preliminary thinning if desired. Then, a STEM probe was used to sculpt more delicate features, including nanowires of approximately 20 nm in width, point contacts, and T-shaped junctions. During STEM cutting, the structures were monitored using energy dispersive X-ray spectroscopy (EDS) mapping, electron diffraction, and high-resolution imaging, and it was found that the crystal structure remains largely intact. This process opens the way for in-situ determination of the effects of size and structure on electrical and thermal properties of Bi$_2$Se$_3$ and fabrication of nanodevices with more elaborate geometries than can be achieved with growth methods alone. [Preview Abstract] |
Friday, March 17, 2017 12:39PM - 12:51PM |
Y8.00008: Possible Gating on the Surface of a Weak Topological Insulator: Bi$_{14}$Rh$_{3}$I$_{9}$ Madhav Prasad Ghimire, Manuel Richter Recently synthesized Bi$_{14}$Rh$_{3}$I$_{9}$ was predicted to be a weak topological insulator. Scanning tunneling microscopy confirms this with a signatures of one-dimensional conducting states in the band gap at step edges of [(Bi$_{4}$Rh)$_{3}$I]$^{2+}$ (2DTI) surface layers. However, the surface-layer gap is found 0.25 eV below the Fermi level ($E_{F})$. Transport experiments are expected to be biased by intrinsic n-doping at the surface. Using density functional theory slab calculations we resolve this issue to shift $E_{F\, }$into the surface layer gap without losing its topological properties. We perform chemical modification on the surface of Bi$_{14}$Rh$_{3}$I$_{9}$: sparse layer of Iodine atoms is added onto the 2DTI surface. Investigation shows that deposition of one I atom per surface unit cell onto 2DTI surface opens a surface gap of 0.1 eV at $E_{F}$, if simultaneously one I atom is removed from the dorsal spacer layer. The same effect with reduced gap size (0.08 eV) is observed for adding/removing I atoms in two fold higher concentration. Comparing our results with the experiment [ACS Nano, 2016] we predict that Fermi level can be shifted to the surface gap by deposition of I atoms onto the 2DTI surface in an appropriate range of concentration. [Preview Abstract] |
Friday, March 17, 2017 12:51PM - 1:03PM |
Y8.00009: Thorium Doped CsI: Implications for the Thorium Nuclear Clock Transition E. R. Meyer, E. Timmermans, S. Rudin, J. D. Kress, L. A. Collins, X. Zhao For the 229mTh isomer nucleus, with an anomalously low excitation energy of E*$=$7.8 eV, the bound internal conversion (BIC) decay process is caused by the excitation of a valence electron that is sensitive to the electronic structure of the atomic-sized neighborhood. So to obtain the minimal nuclear excitation energy E*min necessary for BIC-promoting the s-wave valence electron, we analyze a recent experiment of a Th-impurity deposited in a CsI matrix. Depending on whether the Th-impurity is imparted into the bulk, or only a few atomic layers into the (111)-surface, we find that the E*min-value, which is the gap between the Th-s-band and the conduction band minimum (in the large unit cell limit) is equal to 1.4 and 1.7 eV respectively. This number can significantly reduce the lower E*-bound of 6.8 eV, that is the first ionization potential of an isolated Th-atom, as estimated from the recent direct observation of the Th-clock transition (von der Wense et al., Nature 533, 47-51, 2016). We suggest coating the multi-channel plate with materials of different Th-impurity gaps can further narrow the E* uncertainty interval. [Preview Abstract] |
Friday, March 17, 2017 1:03PM - 1:15PM |
Y8.00010: Abstract Withdrawn
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Friday, March 17, 2017 1:15PM - 1:27PM |
Y8.00011: Weyl phonons in transition-metal compounds Tiantian Zhang, Zhida Song, Hongming Weng, Chen Fang, Ling Lu, Zhong Fang Topological phononic crystal (TPC) is the solid-state material having nontrivial topology in its phonon spectrum.We propose that a family of transition-metal compounds be TPC and their phonon dispersions are predicted in ab initio calculations. The symmetry protected Weyl nodes and Dirac nodes at high symmetry momenta have been found by Wilson loop method and k.p model analysis.The open arcs of the isofrequency contour of the surface state extend across the whole surface Brillouin zone,distinguished from all known topological Weyl materials, including Weyl semimetals and Weyl photonic crystals. [Preview Abstract] |
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