Bulletin of the American Physical Society
APS March Meeting 2013
Volume 58, Number 1
Monday–Friday, March 18–22, 2013; Baltimore, Maryland
Session U9: Three Dimensional Topological Insulators: Chalcogenides and New Materials |
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Sponsoring Units: DCMP Chair: Phillip King, Cornell University Room: 308 |
Thursday, March 21, 2013 11:15AM - 11:27AM |
U9.00001: Spin Control of the topological surface states in 3D topological insulators using polarized light Anna Gura, Jeff Secor, Milan Begliarbekov, Lukas Zhao, Haiming Deng, Lia Krusin-Elbaum The topological surface states of 3D topological insulators (TIs)been shown to interact non trivially with circularly polarized light. Here we report on the study of spin-polarized currents in several $2^{nd}$ generation TIs, such as Sb$_2$Te$_3$, Be$_2$Te$_3$, and Bi$_2$Se$_3$. In particular, to probe the robustness of the helical current surface states we will contrast the polarization dependence of the photocurrent in as grown crystals and crystals with controlled disorder introduced by magnetic and non-magnetic impurities. These result in the development of a gap in the energy spectrum of surface Dirac fermions (DFs), that is DFs acquire mass. The photo-response contrast between massless and massive Dirac fermions studied under electric field gating conditions will be presented. [Preview Abstract] |
Thursday, March 21, 2013 11:27AM - 11:39AM |
U9.00002: Highly tunable electron transport in epitaxial topological insulator (Bi$_{1-x}$Sb$_{x})_{2}$Te$_{3}$ thin films Tong Guan, Xiaoyue He, Kehui Wu, Yongqing Li Three dimensional topological insulators (TI) have potential applications in quantum computation and spintronics. These applications often require an insulating bulk and high tunability in chemical potential. Remarkable progresses have been made in synthesizing new TI material with more insulating bulk by alloying the binary compounds Bi$_{2}$Se$_{3}$, Sb$_{2}$Se$_{3}$, Bi$_{2}$Te$_{3}$ and Sb$_{2}$Te$_{3}$ in the past couple of years. Here we report the growth of single crystalline (Bi$_{1-x}$Sb$_{x})_{2}$Te$_{3}$ films on SrTiO$_{3}$(111) substrates by molecular beam epitaxy. A full range of Sb-Bi compositions have been studied. Optimal Sb composition for minimum bulk conduction was found to be x $=$ 0.5 $\pm$ 0.1. For the samples (Bi$_{0.5}$Sb$_{0.5})_{2}$Te$_{3}$, the carrier density can be tuned from n-type to p-type with the help of a back-gate. Linear magnetoresistance has been observed at gate voltages close to the maximum in the longitudinal resistance of (Bi$_{0.5}$Sb$_{0.5})_{2}$Te$_{3}$ sample. These highly tunable (Bi$_{1-x}$Sb$_{x})_{2}$Te$_{3}$ thin films provide an excellent platform to explore the intrinsic transport properties of the three dimensional topological insulators. [Preview Abstract] |
Thursday, March 21, 2013 11:39AM - 11:51AM |
U9.00003: Iodine doping of p-type topological insulators Inna Korzhovska, Lukas Zhao, Haiming Deng, Chen Zhiyi, Lia Krusin-Elbaum We report on the systematic iodine (I) doping of the `intrinsically' \textit{p}-type $2^{nd}$ generation topological insulator (TI) Sb$_2$Te$_3$. Iodine will introduce additional holes into the system and thus pull the Fermi level $E_F$ `down' from the Dirac point. Further, at a sufficient hole density, particle correlation effects are also expected to emerge. Iodine was incorporated into Sb$_2$Te$_3$ using two methods: (i) post-growth vapor exposure of crystals grown by the Vapor-Liquid-Solid (VLS) technique and (ii) \textit{in-situ} doping of crystals grown in a modified Bridgman setup. The first method is self-limiting and only up to 2 at\% iodine is entered, however the \textit{in-situ} doping allowed us to increase iodine content up to 20\%. Detailed XRD Rietveld refinement analysis of the doped crystals doping indicates that for the I-content greater than 10\% the rhombohedral structure is modified to reflect some extent of the I-Te and I-Sb bonding. We find that iodine doping affects the large diamagnetic susceptibility, particularly at low magnetic fields. Our measurements of Hall resistivity confirm that under doping resistivity remains \textit{p}-type. The contrasting effects of the iodine doping into the intrinsically \textit{n}-type Bi$_2$Se$_3$ will be presented. [Preview Abstract] |
Thursday, March 21, 2013 11:51AM - 12:03PM |
U9.00004: Nuclear Magnetic Resonance Studies of Bulk States of Bi2Se3 D.M. Nisson, A.P. Dioguardi, P. Klavins, C.H. Lin, K. Shirer, A. Shockley, J. Crocker, N.J. Curro We present $^{209}$Bi nuclear magnetic resonance (NMR) spectra and relaxation rate data on single crystals of Bi$_{2}$Se$_{3}$ grown under various conditions, whose carrier concentrations, resistivities, and Shubnikov-de Haas (SdH) frequencies have been measured. Our NMR data reveal properties of the bulk states, which are influenced by the presence of intrinsic carriers. We find that both the Knight shift and the electric field gradient of the Bi is correlated with carrier concentration, and atypical spectral profiles. Surprisingly, spin-lattice relaxation is not strongly temperature dependent. [Preview Abstract] |
Thursday, March 21, 2013 12:03PM - 12:15PM |
U9.00005: Origin of helical spin texture of topological phase transition family materials TlBi(Se$_{1-x}$S$_{x}$)$_{2}$ Justin Waugh, Yue Cao, Koji Miyamoto, Taichi Okuda, Chetan Dhital, Stephen Wilson, Daniel Dessau The unique helically spin-polarized metallic surface states of topological insulators are believed to arise from an odd number of band inversions per unit cell. It is believed that the band inversion in the family of compounds TlBi(Se$_{1-x}$S$_{x}$)$_{2}$ can be removed by replacing Se by S, removing the spin-polarized surface states. Using spin and angle-resolved photoemission spectroscopy we here show that even on the gapped non-topological ``trivial'' side of the phase transition (x=0.7), Dirac-like helical spin polarization still exist, as well as small but finite gaps on the topological side of the phase transition (x=0.3). Additional spin helicity inversions are also present in the bulk bands of both samples. We consider various explanations for this effect, including a superposition of domains, massive Dirac states due to thin domains, and Rashba spin orbit splitting at the surfaces. [Preview Abstract] |
Thursday, March 21, 2013 12:15PM - 12:27PM |
U9.00006: Terahertz Quantum Hall Effect of Dirac Fermions in a Topological Insulator A. Pimenov, A. Shuvaev, G. Astakhov, G. Tkachov, Ch. Bruene, H. Buhmann, L. W. Molenkamp Using THz spectroscopy in external magnetic fields we investigate the low-temperature charge dynamics of strained HgTe, a three dimensional topological insulator. From the Faraday rotation angle and ellipticity a complete characterization of the charge carriers is obtained. In resonator experiments, we observe quantum Hall oscillations at THz frequencies. The 2D density estimated from the period of these oscillations agrees well with direct transport experiments on the topological surface state. The Dirac character of the surface state is proven by the observation of a half-integer plateau in the quantum Hall effect. [Preview Abstract] |
Thursday, March 21, 2013 12:27PM - 12:39PM |
U9.00007: Various Types of Dirac Cone Materials of Bi$_{1-x}$Sbx Thin Films Shuang Tang, Mildred Dresselhaus The band structure of bismuth antimony thin films varies as a function of stoichiometry, film thickness and growth orientation. Different types of Dirac cone materials can be constructed based on the bismuth antimony thin films system, including single-Dirac-cone, bi-Dirac-cone and tri-Dirac cone materials, and also including exact-Dirac-cone, semi-Dirac-cone and quasi-Dirac-cone materials. The degree of anisotropy of a Dirac cone can be controlled, which range from $\sim$ 2 to $\sim$ 14. Interesting transport phenomena are expected in different Dirac cone materials, which may be optimized for different purposes of applications, e.g. thermoelectrics, electronics etc. [Preview Abstract] |
Thursday, March 21, 2013 12:39PM - 12:51PM |
U9.00008: Dirac fermions, Fermi surface and magnetotransport in bulk crystals of layered SrZnSb2 Kefeng Wang, Limin Wang, David Graf, Cedomir Petrovic We report evidence for anisotropic Dirac-like pockets and the large magnetoresistance in the quasi-two-dimensional Sb rectangular layers of bulk SrZnSb2 crystals. Due to the two-fold symmetry of the Sb layers, there are three different Dirac-like pockets as revealed by the calculated Fermi surface. Angular dependent in-plane magnetoresistance and oscillation frequencies indicate the quasi-two-dimensional character of the pockets. This is different from the identical Dirac-cone-like points in the Bi square net of SrMnBi2. The large linear magnetoresistance and magnetothermopower were observed in crystals. The magnetoresistance behavior can be described very well by combining the semiclassical cyclotron contribution and the quantum limit magnetoresistance. Magnetic field also enhances the thermopower. Our results can be well understood by the magnetotransport of Dirac states in the bulk band structure. Work at BNL supported by Office of Basic Energy Sciences, US DOE, under contract No. DE-AC02-98C (K. W, L. W and C. P.). Work at the National High Magnetic Field Laboratory is supported by the DOE NNSA DE-FG52-10NA29659, by the NSF Cooperative Agreement No.DMR-0654118, and by the state of Florida (D. G.) [Preview Abstract] |
Thursday, March 21, 2013 12:51PM - 1:03PM |
U9.00009: $\beta -$Ag$_{2}$Te: A topological insulator with strong anisotropy Lan Wang, Azat Sulaev, Peng Ren, Bin Xia, Qinghua Lin, Ting Yu, Caiyu Qiu, Shuang-yuan Zhang, Ming-Yong Han, Zhipeng Li, Wei Guang Zhu, Qingyu Wu, Yuan Ping Feng, Lei Shen, Shun-Qing Shen We present evidence of topological surface states in $\beta $-Ag$_{2}$Te through first-principles calculations, periodic quantum interference effect and ambipolar electric field effect in single crystalline nanoribbon. Our first-principles calculations show that $\beta $-Ag$_{2}$Te is a topological insulator with a gapless Dirac cone with strong anisotropy. To experimentally probe the topological surface state, we synthesized high quality $\beta $-Ag$_{2}$Te nanoribbons and performed electron transport measurements. The coexistence of pronounced Aharonov-Bohm oscillations and weak Altshuler-Aronov-Spivak oscillations clearly demonstrates coherent electron transport around the perimeter of $\beta $-Ag$_{2}$Te nanoribbon and therefore the existence of topological surface states, which is further supported by the ambipolar electric field effect for devices fabricated by $\beta $-Ag$_{2}$Te nanoribbons. The experimentally confirmed topological surface states and the theoretically predicted isotropic Dirac cone of $\beta $-Ag$_{2}$Te suggest that the material may be a promising material for fundamental study and future spintronic devices. [Preview Abstract] |
Thursday, March 21, 2013 1:03PM - 1:15PM |
U9.00010: Topological Surface State Observed in Superconducting (Ir1-xPtx)Te2 Tian Qian, Hu Miao, Gang Xu, Xi Dai, Zhong Fang, Aifa Fang, Nanlin Wang, Hong Ding Topologically non-trivial surface state is the hallmark of 3D topological insulators and topological superconductors, where spin-orbit coupling (SOC) plays an essential role. By Ir site doping of 5{\%} Pt, the huge SOC material IrTe2 becomes a superconductor with maximal Tc $=$ 3K. Our angle resolve photoemission spectroscopy (ARPES) study combined with LDA analysis demonstrate the surface states of (Ir1-xPtx)Te2 is toplogically non-trivial. [Preview Abstract] |
Thursday, March 21, 2013 1:15PM - 1:27PM |
U9.00011: Transport properties of crystalline topological insulator Pb$_{1-x}$Sn$_x$Se Tian Liang, Quinn Gibson, Jun Xiong, M.A. Hirschberger, R.J. Cava, N.P. Ong The narrow-band gap semiconductors Pb$_{1-x}$Sn$_x$Se and Pb$_{1-x}$Sn$_x$Te have received considerable attention recently following the prediction~[1] that they are examples of a topological crystalline insulator with surface states characterized by a mirror Chern number. Several ARPES groups have reported evidence for the topological surface states~[2,3]. We have investigated the transport properties of crystals of Pb$_{1-x}$Sn$_x$Se. For Sn content $x$ bracketing 0.23, we observe strong quantum oscillations from bulk carriers (either $n$ or $p$ type) with concentrations near 2$\times 10^{18}$ cm$^{-3}$ and mobilities $\sim $ 3,000 cm$^2$/Vs. The results of experiments to tune the chemical potential into the gap using chemical doping and liquid gating will be reported. References: [1] T. H. Hsieh et al., Nature Commun. {\bf 3}, 982 (2012). [2] P. Dziawa et al., Nature Materials (2012) doi:10.1038/nmat3449 [3] Su-Yang Xu et al., arXiv:1206.2088 [Preview Abstract] |
Thursday, March 21, 2013 1:27PM - 1:39PM |
U9.00012: NMR Studies of the Candidate Topological Superconductor Sn$_{1-x}$In$_{x}$Te: Spin-Triplet Superconductivity Robust against Magnetic Impurities X.R. Lu, L. Ma, J. Dai, P. Wang, B. Normand, W. Yu, R.D. Zhong, J. Schneeloch, Z.J. Xu, G.D. Gu In-doped SnTe is a low-carrier-density semiconductor with strong spin-orbit coupling, and has been proposed to be a topological superconductor. We report nuclear magnetic resonance (NMR) studies of both $^{119}$Sn and $^{125}$Te nuclei, performed on single crystals of Sn$_{1-x}$In$_{x}$Te, where $T_c = 1.8$ K for $x = 0.1$. Under an applied field of 0.33 T, the spin-lattice relaxation rate $1/^{119}T_1$ drops rapidly below 1.2 K, indicating bulk superconductivity. We observe absolutely no change in the Knight shift with temperature when $T < T_c$, which in NMR is normally an indicator of spin-triplet superconductivity. We find no coherence peak below $T_c$ in $1/^{119}T_1$, suggesting an unconventional order parameter but also the possible role of impurities. In the normal state we find that $1/^{119}T_1$ and $1/^{125}T_1$ have Fermi-liquid behavior at high fields, but at low fields show a large Curie-Weiss-type enhancement indicative of magnetic impurity effects. Thus the fact that $T_c$ in our samples is insensitive to the sample purity suggests that superconductivity in Sn$_{1-x}$In$_{x}$Te is robust against magnetic impurities, in contrast to the situation in conventional superconductors. [Preview Abstract] |
Thursday, March 21, 2013 1:39PM - 1:51PM |
U9.00013: Electronic Structure Study on a 3D Dirac Semimetal Candidate Y.L. Chen, Z.K. Liu, B. Zhou, S.K. Mo, D. Prabhakaran, Z.J. Wang, Z. Fang, X. Dai, Z.X. Shen, Z. Hussain A family of 3D Dirac semimetals candidates (A3Bi, A$=$alkali metal, B$=$As, Sb, or Bi) have recently been predicted to exist at the phase transition between a topological and a normal insulator when inversion symmetry is preserved. In such a semimetal, the conduction and valence bands touch only at Dirac points around which the dispersion is linear in all directions, leading to distinct physical properties, such as giant diamagnetism and linear quantum magneto-resistance. We used angle resolved photoemission spectroscopy (ARPES) to study a 3D Dirac semimetal candidate, Na3Bi and revealed interesting electronic structures. We will discuss our observation, its possible topological origin and the connection to recent theory investigation. [Preview Abstract] |
Thursday, March 21, 2013 1:51PM - 2:03PM |
U9.00014: Competing Orders in the Surface State of Topological Kondo Insulators Jeffrey Botimer, Dae-Jeong Kim, Sean Thomas, Zachary Fisk, Jing Xia The recent discovery of topological (band) insulators (TI) reveals a conceptually new family of quantum materials with novel properties. The bulk energy gap closes at the surface, leading to a gap-less metallic topological surface state. Recently several Kondo insulators have been theoretically proposed in this category, dubbed ``Topological Kondo Insulators'' (TKI). In a TKI, the topological order arises from strong electron correlation and will display new physics. For example, various broken symmetry orders are expected to compete with the topological order. In this talk we will present electrical transport evidence for a high mobility conducting surface state, as well as magneto-optic evidence for broken time reversal symmetry at the surface of several TKI materials. These results suggest that the surface state of the TKI are not only topological but also magnetic, thus providing a convenient system to study topological magneto-electric effects where magnetization can be induced by pure electric field. [Preview Abstract] |
Thursday, March 21, 2013 2:03PM - 2:15PM |
U9.00015: Transport Signature of Floquet Majorana Fermions Arijit Kundu, Babak Seradjeh It has been recently predicted that a periodically-driven superconducting quantum wire can support unpaired Floquet Majorana fermions (FMFs), steady-state equal mixtures of electrons and holes bound to the ends of the wire. We further study this proposition and elucidate the range of parameters and drives that give rise to FMFs. We also look for possible transport signatures of FMFs within a non-equilibrium Green's function approach. We analyze the conductance profile for different driving schemes and compare the behavior with that of the static system. We comment on possible experimental setups to observe and exploit FMFs in quantum information processing. [Preview Abstract] |
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