Bulletin of the American Physical Society
APS March Meeting 2015
Volume 60, Number 1
Monday–Friday, March 2–6, 2015; San Antonio, Texas
Session B10: Topological Insulators - Materials and Structures (Theory) |
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Sponsoring Units: DCMP Chair: Arijit Kundu, University of Indiana, Bloomington Room: 007A |
Monday, March 2, 2015 11:15AM - 11:27AM |
B10.00001: Numerical studies on the robustness of the topological surface modes of the topological insulator nanostructures Hsiu-Chuan Hsu, Ajit Coimbatore Balram, Jainendra Jain, Chaoxing Liu It has been found experimentally that the magnetoconductance oscillates as a function of the magnetic flux with a period of $\phi_0$ ($\phi_0=h/e$, one flux quantum) in strongly disordered topological insulator (TI) nanotubes. In an effort to understand the origin of the oscillation, we calculate the magnetoconductance of TI nanowire and nanotube within the Landauer formalism at different disordered strengths and Fermi levels. We found unambiguous oscillation features of the magnetoconductance which survive even in extreme disordered regime. The oscillation is attributed to the occurrence of gapless helical surface modes when the surface encloses a magnetic flux of integer multiples of $\phi_0/2$. These features demonstrate a robust transport signature of the helical surface mode(s) of the TI nanostructures. [Preview Abstract] |
Monday, March 2, 2015 11:27AM - 11:39AM |
B10.00002: Wire deconstructionism of two-dimensional topological phases Ronny Thomale, Titus Neupert, Claudio Chamon, Christopher Mudry A scheme is proposed to construct integer and fractional topological quantum states of fermions in two spatial dimensions. We devise models for such states by coupling wires of non-chiral Luttinger liquids of electrons, that are arranged in a periodic array. Which inter-wire couplings are allowed is dictated by symmetry and the compatibility criterion that they can simultaneously acquire a finite expectation value, opening a spectral gap between the ground state(s) and all excited states in the bulk. First, with these criteria at hand, we reproduce the tenfold classification table of integer topological insulators, where their stability against interactions becomes immediately transparent in the Luttinger liquid description. Second, we construct an example of a strongly interacting fermionic topological phase of matter with short-range entanglement that lies outside of the tenfold classification. Third, we expand the table to long-range entangled topological phases with intrinsic topological order and fractional excitations. [Preview Abstract] |
Monday, March 2, 2015 11:39AM - 11:51AM |
B10.00003: From toothpaste to topological insulators and materials for valleytronics: The journeys of fluorinated tin Salvador Barraza-Lopez, Pablo Rivero, Jia-An Yan, Victor Manuel Garcia-Suarez, Jaime Ferrer Tin fluoride has a vast literature [1]. This material is stable in bulk form at room temperature and has commercial applications that include fluorinated toothpaste. Bulk tin fluoride has a pair of fluorine atoms bridging two tin atoms. In the recent past the electronic properties of 2D tin with honeycomb structure have been discussed [2] thus generating a wealth of literature that emphasizes its non-topologically-trivial electronic properties due to the combination of a Dirac-like dispersion and a strong spin-orbit coupling given its large atomic mass [3]. Nevertheless the stability of such freestanding structures has been contested recently [2]. As it turns out, the most stable form of fluorinated tin does not possess a graphane-like structure either [4]. In the most stable phase to be discussed here, fluorine atoms tilt away from (graphane-like) positions over/below tin atoms; in an atomistic arrangement similar to the one seen on their parent bulk structure. Electronic properties depend on atomistic coordination, and the most stable form of fluorinated tin does not possess non-trivial topological properties. Nevertheless it represents a new paradigm for valleytronics in 2D. References: [1] G. Denes, et al. \textit{J. Solid State Chem.} \textbf{33}, 1 (1980). [2] Y. Ma, et al. \textit{J. Chem. Phys. C} \textbf{116}, 12977 (2012); Y. Xu, et al. \textit{PRL} \textbf{111}, 136804 (2013); P. Tang, et al. \textit{PRB} \textbf{90}, 121408(R) (2014). [3] C. L. Kane and E. J. Mele. \textit{PRL} \textbf{95}, 226801 (2005). [4] P. Rivero et al. Submitted on 07/27/14. [Preview Abstract] |
Monday, March 2, 2015 11:51AM - 12:03PM |
B10.00004: Magnetic Susceptibility and Quantum Oscillations in a Buckled Honeycomb Lattice Calvin Tabert, Jules Carbotte, Elisabeth Nicol We calculate the magnetic response of a low-buckled honeycomb lattice with intrinsic spin-orbit coupling which is described by the Kane-Mele Hamiltonian (a model which would describe the low-energy physics of a material like silicene). Included in the Hamiltonian, is a sublattice potential difference term which may be induced by a perpendicular electric field; this field can tune the system from a topological insulator (TI), through a valley-spin polarized metal, to a trivial band insulator (BI). In an external magnetic field, a distinct signature of the phase transition is seen in the derivative of the magnetization with respect to chemical potential; this gives the quantization of the Hall plateaus through the Streda relation. The results are compared with the zero-frequency conductivity obtained from the Kubo formula. The magnetic susceptibility also displays signatures of the different topological phases. We also explore the de-Haas van-Alphen effect. At the transition point between the TI and BI, magnetic oscillations exist for any value of chemical potential. Away from the critical point, the chemical potential must be larger than the minimum gap. For large chemical potential (or small but finite sublattice potential difference), there is a strong beating pattern. [Preview Abstract] |
Monday, March 2, 2015 12:03PM - 12:15PM |
B10.00005: Properties of interacting 2D chiral tensor network states Barry Bradlyn, Jerome Dubail, Nicholas Read In a recent paper, Dubail and Read [1] gave a construction for free fermion tensor network states [2](TNSs) in the \emph{chiral} $p+ip$ and $\nu=1$ Chern insulator topological phases in two dimensions, and gave a generalization to Laughlin-like states. However, on general principles these free fermion states must be ground states of \emph{gapless} local Hamiltonians. In this talk, we address the issue of the energy gap in the interacting states, with a particular focus on the $\nu=1/2$ bosonic Laughlin-like TNS. Through a combination of analytic and numerical arguments, we will show that these states too have gapless local parent Hamiltonians. Nevertheless, we will explore to what degree they can be used as numerical approximations to gapped phases.\\[4pt] [1] J. Dubail and N. Read, arXiv:1307.7726 (2013). \\[0pt] [2] F. Verstraete and J.I. Cirac, cond-mat/0407066 (2004). [Preview Abstract] |
Monday, March 2, 2015 12:15PM - 12:27PM |
B10.00006: Exactly soluble 3D lattice models and the braiding statistics of their loop excitations Chien-Hung Lin, Michael Levin We construct two exactly soluble 3D lattice models that belong to distinct topological phases in the sense that they cannot be smoothly connected without an intervening phase transition. What is interesting is that the two models have very similar physical properties: both are gapped and both support particle-like and loop-like excitations with non-trivial mutual statistics similar to that of charges and vortex lines in a Z2 x Z2 gauge theory. The only difference between the two models lies in the braiding statistics of their loop excitations. As an application of these results, we construct two other closely related spin models with Z2 x Z2 global symmetry. We show that one of these spin models realizes a Z2 x Z2 symmetry protected phase with protected surface states while the other realizes a trivial phase without a protected surface. [Preview Abstract] |
Monday, March 2, 2015 12:27PM - 12:39PM |
B10.00007: Topological phases in Iridium oxide superlattices: quantized anomalous charge or valley Hall insulators Hae-Young Kee, Yige Chen Designing materials is one of intense topics in modern condensed matter physics. Recently, how to achieve a topological insulator in transition metal oxides with strong spin-orbit coupling became an interesting subject. We have investigated possible topological phases in orthorhombic perovskite Iridium (Ir) oxide superlattices grown along the [001] crystallographic axis. We found that bilayer Ir oxide superlattices exhibit quantized anomalous Hall effects in magnetic topological insulating phases. We also found, depending on the stacking of two layers, a valley Hall insulator with nontrivial valley dependent surface modes and a topological crystalline insulator with the crystal symmetry protected edge states can be realized. Experimental tools to detect such topological phases are also discussed. [Preview Abstract] |
Monday, March 2, 2015 12:39PM - 12:51PM |
B10.00008: Surface States of Perovskite Iridates AIrO$_3$; Signatures of Topological Crystalline Metal with Nontrivial $Z_2$ Index Heung-Sik Kim, Yige Chen, Hae-Young Kee There have been increasing efforts in realizing topological metallic phases with nontrivial surface states, including a topological crystalline metal phase with flat surface states suggested recently. Here we perform first-principles electronic structure calculations for epitaxially stabilized orthorhombic perovskite iridates with $Pbnm$ symmetry. Remarkably, two types of distinct topological surface states are found depending on the surface direction. On the side surfaces, flat surface states protected by the mirror symmetry emerge manifesting the topological crystalline character. On the top surface where mirror symmetry is broken, a Dirac cone appears indicating a non-trivial topology of the nodal metal. Indeed, there is a well-defined two dimensional topological $Z_2$ index associated with time reversal symmetry leading to the Dirac surface state. Transitions to weak and strong topological insulators and implications of different surface states in light of angle resolved photoemission spectroscopy are also discussed. [Preview Abstract] |
Monday, March 2, 2015 12:51PM - 1:03PM |
B10.00009: Topological phase transitions in TlBiS$_2$ and TlSbS$_2$ under strain Qingyun Zhang, Yingchun Cheng, Udo Schwingenschlogl Using first-principles calculations, we investigate the band structure evolution and topological phase transitions in TlBiS$_2$ and TlSbS$_2$ under hydrostatic pressure as well as uniaxial and biaxial strain. For TlBiS$_2$ topological transitions occur around 0 and 5 GPa, the system remaining a direct gap semiconductor up to 8 GPa. On the other hand, for TlSbS$_2$ the transitions occur around 2 and 5 GPa and the system transform from a direct gap semiconductor to a semimetal around 2 GPa. Biaxial and uniaxial strains are compared to each other. The phase transitions are identified by parity analysis and by calculating the surface states. Zero, one and four Dirac cones are found for the (111) surfaces of both TlBiS$_2$ and TlSbS$_2$ when increasing the pressure, which confirms the trivial-nontrivial-trivial phase transitions. The Dirac cones at the M points are anisotropic with a large out-of-plane component and inversely related in-plane spin and momentum direction. By examining the states on different surfaces we show that TlBiS$_2$ under 8 GPa pressure is a topological crystalline insulator. This finding makes the thallium-based III-V-VI2 ternary chalcogenides candidates for studies on topological crystalline phase. [Preview Abstract] |
Monday, March 2, 2015 1:03PM - 1:15PM |
B10.00010: A Novel Quasi-One-Dimensional Topological Insulator in Bismuth Iodide $\beta$-Bi$_4$I$_4$: Theoretical Prediction and Experimental Confirmation Oleg V. Yazyev, Gabriel Aut\`{e}s, Anna Isaeva, Luca Moreschini, Jens C. Johannsen, Andrea Pisoni, Taisia G. Filatova, Alexey N. Kuznetsov, L\'{a}szl\'{o} Forr\'{o}, Wouter Van den Broek, Yeongkwan Kim, Jonathan D. Denlinger, Eli Rotenberg, Aaron Bostwick, Marco Grioni A new strong $Z_2$ topological insulator is theoretically predicted and experimentally confirmed in the $\beta$-phase of quasi-one-dimensional bismuth iodide Bi$_4$I$_4$. According to our first-principles calculations the material is characterized by $Z_2$ invariants (1;110) making it the first representative of this topological class. Importantly, the electronic structure of $\beta$-Bi$_4$I$_4$ is in proximity with both the weak topological insulator phase (0;001) and the trivial phase (0;000), suggesting that a high degree of control over the topological electronic properties of this material can be achieved. Experimentally produced samples of this material appears to be practically defect-free, which results in a low concentration of intrinsic charge carriers. By using angle-resolved photoemission spectroscopy (ARPES) on the (001) surface we confirm the theoretical predictions of a highly anisotropic band structure with a small band gap hosting topological surface states centered at the $\bar{M}$ point, at the boundary of the surface Brillouin zone. [Preview Abstract] |
Monday, March 2, 2015 1:15PM - 1:27PM |
B10.00011: ABSTRACT WITHDRAWN |
Monday, March 2, 2015 1:27PM - 1:39PM |
B10.00012: Topological phases in SnTe thin films with a periodic array of defects and charge doping Minsung Kim, Jisoon Ihm In this study, we investigate the topological phases of two-dimensional SnTe thin films with defect superstructures and charge doping. We find that the Sn-Te bilayer is a two-dimensional normal insulator, but can be transformed into a topological insulator by introducing an appropriate array of defects. Also, the topological phases of the films can be further controlled by charge doping due to the narrow bandwidth of the topologically nontrivial defect-induced bands. The results could be useful for the realization and control of the topological phases in nano-scale thin films. [Preview Abstract] |
Monday, March 2, 2015 1:39PM - 1:51PM |
B10.00013: Topological states of non-Dirac electrons on Si[111] surface Rui Yu, Qifeng Liang, Xiao Hu In the present work, we demonstrate the possibility of nontrivial topology of non-Dirac electrons. In particular, we show that, in two dimensional systems with $C_{\rm 3}$ crystal symmetry and time reversal symmetry, multiple $p$-orbits exhibit a degeneracy and quadratic non-Dirac band dispersions at $\Gamma$ point. When the atomic spin-orbit coupling (SOC) is taken into account, a gap is opend at $\Gamma$ point and a quantum spin Hall effect state is realized. We construct a $k\cdot p$ model to reveal the nontrivial topology which is associated with a meron structure with double vorticity in the pseudo spin texture, a mechanism different from that on honeycomb lattice and the band inversion. We propose that Si[111] surface with 1/3 regular coverage of Bi atoms is a realization of our idea. First-principles calculations show that this system takes a quantum spin Hall phase with topological gap as large as $\sim 0.15$eV. [Preview Abstract] |
Monday, March 2, 2015 1:51PM - 2:03PM |
B10.00014: Absence of an interaction driven Chern insulating phase on the honeycomb lattice Johannes Motruk, Adolfo G. Grushin, Frank Pollmann Mean field calculations in the literature have suggested the existence of an interaction-induced Chern insulator (CI) phase in a tight-binding model of spinless fermions on a honeycomb lattice with nearest- and next-nearest-neighbor interactions. The CI phase is an example of a state that breaks time-reversal symmetry spontaneously and possesses a quantized Hall conductance. However, it has been proven elusive in exact diagonalization (ED) studies of this system. Since ED is limited to small system sizes, the fate of this phase in the thermodynamic limit still remains unclear. Using the infinite density matrix renormalization group (iDMRG) algorithm we reach system sizes exceeding those accessible in ED calculations while keeping track of quantum fluctuations neglected in mean field studies. We map out the phase diagram as a function of both nearest- and next-nearest-neighbor interaction strengths for an infinite cylinder geometry and find different charge-ordered phases but no sign of the interaction driven Chern insulator phase. [Preview Abstract] |
Monday, March 2, 2015 2:03PM - 2:15PM |
B10.00015: Chern numbers on the Fermi surface of bcc iron Ivo Souza, Daniel Gos\'albez, David Vanderbilt A metal whose Fermi surface contains sheets with nonzero Chern numbers is topologically nontrivial. This can occur when either spatial inversion ($P$) or time-reversal ($T$) symmetry is broken, and spin-orbit is present. Taking ferromagnetic iron as a prototypical $T$-broken metal, we determine the Chern indices of all the Fermi sheets, starting from a census of the isolated band touchings in the Brillouin zone. Although there are many band touching points carrying a topological charge, the Chern index vanishes for most Fermi sheets. The reason is that they surround $P$-invariant points in the BZ, so that the enclosed band-touching points come in pairs of equal and opposite charge. The exceptions are two small electron pockets on the [001] $\Gamma$H line parallel to the magnetization. Each of them encloses a single Weyl point, leading to Chern indices of $\pm 1$. The contribution of these two pockets to the anomalous Hall conductivity is given, modulo a ${\bf G}$-vector, by their reciprocal-space separation, as in a magnetic Weyl semimetal. In order to resolve the quantum of indeterminacy~${\bf G}$ we plot isocontours of the Berry phase calculated along [010] strings of $k$-points, which carry the same topological information as Fermi arcs in the (010) surface bandstructure. [Preview Abstract] |
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