Bulletin of the American Physical Society
2015 Annual Meeting of the APS Mid-Atlantic Section
Volume 60, Number 14
Friday–Sunday, October 23–25, 2015; Morgantown, West Virginia
Session A4: Topological Insulator |
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Chair: Tudor Stanesu, West Virginia University Room: Waterfront Hotel Salon E |
Saturday, October 24, 2015 10:30AM - 11:06AM |
A4.00001: TBD Invited Speaker: Zahid Hasan . [Preview Abstract] |
Saturday, October 24, 2015 11:06AM - 11:18AM |
A4.00002: Prediction of Weyl semi-metallic phase in inversion-asymmetric BiSb Sobhit Singh, Irais Valencia-Jaime, Andres Garcia-Castro, Francisco Mu\~noz, Aldo Romero Recent experimental realization of long sought Weyl fermions in non-magnetic crystals has greatly motivated the condensed matter physicist to search for the materials supporting Weyl fermions [1-3]. Weyl fermions appear to be very promising for the future electronics, often referred as Weyltronics. By means of first-principle calculations, we report a non-magnetic stoichiometric crystal structure of BiSb with broken space-inversion symmetry. This structure is insulating in bulk and has non-trivial band topology. We observe a pressure driven Weyl semi-metallic phase transition in this structure. The obtained Weyl semi-metallic phase exist in the $4.0 - 6.0$ GPa pressure range. We find that total 12 pairs of Weyl points, 12 monopoles and 12 antimonopoles, exist in the bulk Brillouin zone. The Weyl points with opposite chirality are located at different energy values yielding separate electron and hole Fermi-surfaces which yields novel topological transport properties in this system. [1] Science 349, 622 (2015) [2] Nat Phys 11, 748 (2015) [3] Phys. Rev. X 5, 031013 (2015) [Preview Abstract] |
Saturday, October 24, 2015 11:18AM - 11:30AM |
A4.00003: Quantum Transport Properties of Bi$_{\mathrm{2}}$Se$_{\mathrm{3\thinspace }}$Thin Films Sercan Babakiray, Amit KC, Pavel Borisov, David Lederman We address the surface and bulk electronic transport properties of topological insulator Bi$_{\mathrm{2}}$Se$_{\mathrm{3}}$ thin films in parallel and perpendicular magnetic fields. Bi$_{\mathrm{2}}$Se$_{\mathrm{3}}$ thin films with nominal thickness values of 12, 16, 20 and 25 quintuple layers (QLs) were grown by molecular beam epitaxy (MBE). Epitaxial growth of the films were confirmed by RHEED analysis. Crystal orientation and disorder were studied by XRD scans. XRR was used to confirm the film thickness and roughness. Structural data indicated a slight increase in the disorder with increasing film thickness, but overall the samples were highly crystalline. Weak antilocalization (WAL) was observed in magnetoconductance measurements with the magnetic field applied parallel to the samples' surface and at temperatures between 2 K and 20 K, which indicated a significant contribution to the transport from the bulk states. Large phase coherence lengths with the field applied both perpendicular and parallel to the surface confirmed the diffusive nature of the transport. Quantitatively, the phase coherence lengths (L$_{\mathrm{\emptyset }})$ obtained from the Altshuler-Aronov and Hikami-Nagaoka-Larkin mechanisms were an order of magnitude larger than the film thickness (d) for all of the samples. Parallel magnetoconductance and the corresponding bulk phase coherence lengths were used to estimate the contribution of bulk and surface states in the perpendicular transport. [Preview Abstract] |
Saturday, October 24, 2015 11:30AM - 11:42AM |
A4.00004: \textbf{Optical Properties of Dirac Materials} Dennis Drew Recently strong spin-orbit interaction and topological considerations have led to materials with 3D Weyl or Dirac energy band dispersions. Several novel phases have been predicted for these materials, including fractionalized topological insulators, chiral spin liquids, topological Weyl semimetals, axion insulators and spin liquids. These 3D materials are semimetals corresponding to zero gap semiconductors. As such their optical properties have new features not seen in conventional materials including logarithmic singularities in the dielectric function. We will present preliminary optical studies on several of these new materials. The materials studied include Dirac materials Cd$_{\mathrm{3}}$As$_{\mathrm{2}}$ and Na$_{\mathrm{3}}$Bi and the Weyl semimetal Eu$_{\mathrm{2}}$Ir$_{\mathrm{2}}$O$_{\mathrm{7}}$ which has broken time reversal symmetry in the antiferromagnetic state. The optical data give the first evidence for a Weyl state in Eu$_{\mathrm{2}}$Ir$_{\mathrm{2}}$O$_{\mathrm{7}}$. We also observe the logarithmic singularities associated with the Pauli blocking of the inter Dirac cone excitations in Cd$_{\mathrm{3}}$As$_{\mathrm{2}}$ and Na$_{\mathrm{3}}$Bi. These optical data provides important information about the 3D energy band structure of these novel materials that are not amenable to surface probes such as ARPES or STM. [Preview Abstract] |
Saturday, October 24, 2015 11:42AM - 11:54AM |
A4.00005: All-optically injected photocurrents in topologically insulating Bi2Se3 Derek Bas, Rodrigo Muniz, Sercan Babakiray, Tudor Stanescu, David Lederman, John Sipe, Alan Bristow Nonlinear optics techniques have been employed to provide an all-optical method to generate and control photocurrents in semiconductors. Inevitably arises the challenge of distinguishing various processes that contribute to the photocurrent. This talk reports the generation of shift and injection currents simultaneously in topologically insulating bismuth selenide (Bi2Se3) thin films. A near-infrared pump and its phase-related frequency-doubled counterpart excite the currents, which are detected through their terahertz radiation. The properties of the photocurrents, such as their magnitude and direction relative to the polarization of the incident fields, are compared to theoretical predictions based on the symmetries of the crystal lattice, allowing the different photocurrents to be isolated. This work thus presents a comprehensive all-optical method for analyzing the optoelectronic properties of topological insulators. [Preview Abstract] |
Saturday, October 24, 2015 11:54AM - 12:06PM |
A4.00006: Probing Quantum Anomalous Hall Edge States in Cr doped (Bi,Sb)$_{\mathrm{2}}$Te$_{\mathrm{3}}$ Topological Insulators Anthony Richardella, Abhinav Kandala, Chaoxing Liu, Nitin Samarth The quantum anomalous Hall (QAH) effect is one of the most dramatic demonstrations of the topological properties of topological insulators. Similar to the quantum Hall effect, magnetically doped topological insulators can show a quantized conductance but with no external applied field required. We discuss the growth of these materials by molecular beam epitaxy (MBE) and characterization of their structural and transport properties. While truly quantized conduction usually requires dilution fridge temperatures, there is much interest in trying to push this effect to higher temperatures. Defects and sample degradation from exposure to atmosphere or processing during device fabrication will be discussed. We also show that, using the unusual angular dependence of the anisotropic magnetoresistance (AMR) from tilted field measurements, contributions from bulk and edge transport can be separated. This gives us information about the scattering of electrons between bulk and edge channels that can be used to characterize how the transport evolves as a function of temperature. [Preview Abstract] |
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