Bulletin of the American Physical Society
APS March Meeting 2018
Monday–Friday, March 5–9, 2018; Los Angeles, California
Session K08: Topological Insulators: Transport and Optical properties 
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Sponsoring Units: DCMP Room: LACC 153C 
Wednesday, March 7, 2018 8:00AM  8:12AM 
K08.00001: Characterization of a Highly BulkResistive Topological Insulator and Carrier Control by External Gating Tetsuro Misawa, Yasuhiro Fukuyama, Shuji Nakamura, Yuma Okazaki, Nariaki Nasaka, Chiharu Urano, NobuHisa Kaneko, Takao Sasagawa On the surface of a topological insulator, kinds of novel phenomena are expected, owing to the exotic band structure with the Dirac fermion. An observation of transport properties on surfaces of a topological insulator is generally difficult because massive bulk carriers covers up the surface signals. In order to suppress the bulk transport, several new materials with high bulk resistivity have been suggested. Among them, Sndoped BiSbTe_{2}S (SnBSTS) is a promising material with a particularly large activation energy, which even reaches 150 meV. This is more than twice that of formerlyknown highlyresistive ones, e.g. BiSbTeSe_{2}. We synthesized single crystals of SnBSTS by the modified Bridgman method and characterized their electric transport properties. We thinned the crystals and made it in Hall devices. In the thinned crystal, the top and the bottom surfaces form transport channels, which we controlled individually by applying gate voltage. We used a thermal oxidation layer of SiO_{2} on the Si substrate as the insulating layer for the back gate and used an ionic liquid for the top gate. Successful control of carrier types on the surfaces will be presented. 
Wednesday, March 7, 2018 8:12AM  8:24AM 
K08.00002: Terahertz modulation of the transport properties of surface states of a 3D Topological Insulator Puja Mondol, Sankalpa Ghosh, Manish Sharma

Wednesday, March 7, 2018 8:24AM  8:36AM 
K08.00003: Currentinduced Gap Opening in Interacting Topological Insulators Ajit Coimbatore Balram, Karsten Flensberg, Jens Paaske, Mark Rudner Gapping the conducting surface states of topological insulators (TIs) by time reversal symmetry breaking perturbations, such as coupling to a ferromagnet or circularly polarized light, is important for realizing a variety of intriguing new phenomena in these exotic materials. Here we propose a new mechanism for gapping TI surface states, using applied DC currents. The currentcarrying nonequilibrium state breaks timereversal symmetry, and furthermore hosts a nontrivial spin polarization due to strong spinorbit coupling. Due to electronelectron interactions, this spin polarization produces an internal exchange field that breaks the degeneracy between Kramers partner states. We illustrate this gap opening mechanism for onedimensional quantum spin Hall edge states and twodimensional Dirac surface states, and discuss the parameters that control the size of the induced gaps as well as experimental signatures. 
Wednesday, March 7, 2018 8:36AM  8:48AM 
K08.00004: Mesoscopic Fluctuations of Conductance in Topological Crystalline Insulators Rodney Snyder, Christie Trimble, Samuel Deitemyer, Charles Rong, Patrick Folkes, Patrick Taylor, James Williams Topological crystalline insulators (TCI) offer a path to topological states of matter with a distinct character compared to timereversal invariant topological insulators. Recent work by our group [arxiv.org/abs/1710.06077] suggests the possibility of disorderinduced helical modes in Pb1xSnxTe Josephson junctions. To further investigate these modes, we fabricate Pb1xSnxTe devices to measure mesoscopic fluctuations of conductance. Reports of the universal conductance fluctuations and nonlocal conductance will be given as a function of Sn doping on either side of the topological phase transition known to exist at x~0.75. 
Wednesday, March 7, 2018 8:48AM  9:00AM 
K08.00005: Direct Observation of Surface State Thermal Oscillations in SmB_{6} Oscillators Brian Casas, Alexander Stern, Dmitry Efimkin, Jing Xia, Zachary Fisk SmB_{6} is a mixed valence Kondo insulator that has been proposed to be a topological Kondo Insulator with a Kondo insulating gap in the bulk and a gapless Dirac state on the surface. Exploiting its nonlinear dynamics, a tunable SmB_{6} oscillator device was recently demonstrated, where a small DC current generates large oscillating voltages at frequencies from a few Hz to hundreds of MHz. This behavior was explained by a theoretical model describing the thermal and electronic dynamics of coupled surface and bulk states. Here we report direct measurements of the timedependent surface state temperature in SmB_{6} with a RuO_{2} microthermometer. Our results agree quantitatively with the theoretically simulated temperature waveform, and hence support the validity of the oscillator model, which will provide accurate theoretical guidance for developing future SmB_{6} oscillators at higher frequencies. 
Wednesday, March 7, 2018 9:00AM  9:12AM 
K08.00006: Observation of cyclotron antiresonance in topological insulator Bi_{2}Te_{3}. Sasa Dordevic, Hechang Lei, Cedomir Petrovic, Jonathan Ludwig, Dmitry Smirnov We report on the experimental observation of a cyclotron 
Wednesday, March 7, 2018 9:12AM  9:24AM 
K08.00007: Electrical detection of surface state spin polarization of candidate topological Kondo insulator SmB_{6} Jehyun Kim, Chaun Jang, Xiangfeng Wang, Johnpierre Paglione, Seokmin Hong, Dohun Kim SmB_{6} is an example of Kondo insulator compound where hybridization between conduction and core band electron level induces a gap at low temperature. Recently this material system has emerged as a strong candidate for a realization of topologically nontrivial state of matter in strongly correlated system, the topological Kondo insulator, which can be novel platform for investigating interplay between nontrivial topology and correlation driven emergent phenomena in solid state system. While the property of surface conduction with bulk insulating nature at low temperature has been revealed through electronic transport measurement, until now, there has been no direct electronic transport measurement which shows spin momentum locking on the surface of SmB_{6}. In this presentation, I will discuss potentiometric spin voltage measurement performed on the surface of SmB_{6}. Applied current, temperature and an external magnetic field dependence of the spin voltage are consistent with spinmomentum locking property, which can support that the surface state of SmB_{6} is metallic surface with chiral spin texture. 
Wednesday, March 7, 2018 9:24AM  9:36AM 
K08.00008: Observation of Superparamagnetism in Coexistence with Quantum Anomalous Hall C=±1 and C=0 Chern States Ella Lachman, Masataka Mogi, Jayanta Sarkar, Aviram Uri, Kousik Bagani, Yonathan Anahory, Yuri Myasoedov, Martin Huber, Atsushi Tsukazaki, Masashi Kawasaki, Yoshinori Tokura, Eli Zeldov Simultaneous transport and scanning nanoSQUIDontip magnetic imaging studies in Cr(Bi,Sb)_{2}Te_{3} modulationdoped films reveal the presence of superparamagnetic (SPM) order within the quantum anomalous Hall (QAH) regime. SPM dynamics of weakly interacting nanoscale magnetic islands is observed both in the transition regions as well as within the fully quantized C=±1 Chern plateaus. Modulation doping of the topological insulator films is found to give rise to significantly larger SPM islands as compared to uniform magnetic doping, evidently leading to enhanced robustness of the QAH effect. Even in this more robust quantum state, attaining full quantization of transport coefficients requires magnetic alignment of at least 95% of the SPM islands. 
Wednesday, March 7, 2018 9:36AM  9:48AM 
K08.00009: Quantum Hall effect and magnetic topological phase transition in ultralow carrier density Sb_{2}Te_{3} films Maryam Salehi, Jisoo Moon, Deepti Jain, Pavel Shibayev, Seongshik Oh In 2014, the quantum Hall effect (QHE) originated from topological surface states (TSS) was observed for backgated BiSbTeSe_{2 }singlecrystal and shortly after for backgated MBEgrown (Bi_{1−x}Sb_{x})_{2}Te_{3 }films. A year later, with the aid of proper insulating bufferlayer as a growth template along with novel growth methodology, we reported TSSoriginated QHE in large area defectsuppressed MBEgrown Bi_{2}Se_{3} films (sheet carrier density as low as ~7×10^{11 }/cm^{2}) with vanishing longitudinal resistance in absence of gating and without adding impurity. However, for all aforementioned cases, a high magnetic field was required to observe the QHE phenomena. Extending the buffer layer scheme to telluride system allowed us to achieve Sb_{2}Te_{3} thin films with even lower defect density (carrier density as low as ~1.5×10^{11 }/cm^{2}) which eventually led to observation of QHE (without application of gating) at much lower magnetic field of ~5T which is ~5 times lower than the required field for observing QHE in pure binary selenide system of Bi_{2}Se_{3}. Moreover, these samples demonstrate topological phase transition under higher magnetic fields. In this talk, I will discuss the growth procedure and novel magnetotransport properties of these ultralow defectdensity Sb_{2}Te_{3} films. 
Wednesday, March 7, 2018 9:48AM  10:00AM 
K08.00010: Toward high temperature quantum anomalous Hall effect through interface engineering Deepti Jain, Maryam Salehi, Jisoo Moon, Seongshik Oh The experimental realization of quantum anomalous Hall effect (QAHE), i.e. the observation of quantized Hall resistance and zero longitudinal resistance in the absence of an external magnetic field, remained elusive for a long time after its theoretical prediction (Yu.R. et al, Science, 329, 6164, (2010)). It was first observed in magnetically doped topological insulators (Zhang. C.Z. et al, 340,167170 (2013)). One of the main hinderances in observing QAHE has been material defects. Until now, methods such as band engineering, gating effects and modulation doping have been employed to overcome this problem. A major contributor to defects which has been overlooked so far in observing QAHE, is chemical and structural mismatch between the substrate and the sample. In this talk, we will show that the film quality can be substantially improved by introducing a structurally and chemically matched buffer layer. We will further discuss whether this new interface engineering scheme can also help boost the operation temperature of QAHE beyond the present limitation (~1K). 
Wednesday, March 7, 2018 10:00AM  10:12AM 
K08.00011: Topological semimetal realized in a specific honeycomb lattice Simin Nie, Gang Xu, Friedirich Prinz, Shoucheng Zhang As one type of the elementary particles in standard mode, the realization of Weyl fermions in condensed matter has attracted increasing interest. However, most discovered Weyl semimetals show complicate electronic structures, which lead to many confusions for their essential physics. Here we report firstly that fruitful topological phases can be realized in a specific honeycomb lattice, including ideal Weyl semimetal, 3D strong topological insulator, nodalline semimetal, and a novel semimetal consisting of both Weyl nodes and nodallines. Guiding by this model, we demonstrate that GdSI is the longpursuing ideal Weyl semimetal with the least Weyl nodes residing at the Fermi level, and LuSI (YSI) is a 3D strong topological insulator with the righthanded helical surface states. Our work paves a new way to explore the ideal topological semimetals, and provides a good platform to research the physics of the Weyl semimetal and the related device design. 
Wednesday, March 7, 2018 10:12AM  10:24AM 
K08.00012: Phase Diagram in PbSnSe Topological Quantum Wells Gauthier KRIZMAN, Badih Assaf, LouisAnne de Vaulchier, Gérald Bastard, Yves Guldner, Gunther Springholz, Guenther Bauer Topological matter has recently been a wide source of interest as it could provide effective materials for spintronics, quantum information, or ultra fast electronics. Among them, the topological crystalline insulators acquire surface metallic electronic states while their bulk remains insulating. Such surface electrons have the particularity to be two dimension massless Dirac fermions, with a linear dispersion in energy, and are topologically protected against defaults. 
Wednesday, March 7, 2018 10:24AM  10:36AM 
K08.00013: Topological phase transition in noncentrosymmetric semiconductor Te under pressure Toshiya Ideue, Motoaki Hirayama, Hiroaki Taiko, Takanari Takahashi, Masayasu Murase, Takashi Miyake, Shuichi Murakami, Takao Sasagawa, Yoshihiro Iwasa Tellurium is a semiconductor which has the chiral crystal structure without inversion symmetry. Although semiconducting electronic properties and optical properties have been studied over the years, it is attracting renewed interest in recent years due to the noncentrosymmetric crystal structure and strong spinorbit interaction. For example, currentinduced magnetization has been experimentally confirmed [1] and topological phase transition from semiconductor to Weyl semimetal was also theoretically predicted [2]. 
Wednesday, March 7, 2018 10:36AM  10:48AM 
K08.00014: Magnetic Field Influenced ElectronImpurity Scattering and Magnetotransport Jingjing Feng, Cong Xiao, Yang Gao, Qian Niu We formulate a quasiclassical theory ($\omega_c\tau \lesssim 1$ with $\omega_c$ as the cyclotron frequency and $\tau$ as the relaxation time) to study the influence of magnetic field on electronimpurity scattering process in the twodimensional electron gas. We introduce a general recipe based on an abstraction of the detailed impurity scattering process to define the scattering parameter such as the incoming and outgoing momentum and coordinate jump. In this picture, we can conveniently describe the skew scattering and coordinate jump, which will eventually modify the Boltzmann equation. We find an anomalous Hall resistivity different from the conventional BoltzmannDrude result and a negative magnetoresistivity parabolic in magnetic field. The origin of these results will be analyzed. The relevance between our theory and recent simulation and experimental works will be discussed. Our theory dominates in dilute impurity system where the correlation effect is negligible. 
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