Bulletin of the American Physical Society
APS March Meeting 2018
Volume 63, Number 1
Monday–Friday, March 5–9, 2018; Los Angeles, California
Session R17: Graphene and Topological Insulator Surfaces |
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Sponsoring Units: DCMP DMP Chair: James Williams, University of Maryland, College Park Room: LACC 306A |
Thursday, March 8, 2018 8:00AM - 8:12AM |
R17.00001: Quantum spin Hall phase in 2D trigonal lattice Zhengfei Wang, Kyung-Hwan Jin, Feng Liu The quantum spin Hall (QSH) phase is an exotic phenomena in condensed-matter physics. Here we show that a minimal basis of three orbitals (s, px, py) is required to produce a QSH phase via nearest-neighbour hopping in a two-dimensional trigonal lattice. Tight-binding model analyses and calculations show that the QSH phase arises from a spin–orbit coupling (SOC)-induced s–p band inversion or p–p bandgap opening at Brillouin zone centre, whose topological phase diagram is mapped out in the parameter space of orbital energy and SOC. Remarkably, based on first-principles calculations, this exact model of QSH phase is shown to be realizable in an experimental system of Au/GaAs(111), facilitating the possible room-temperature measurement. Our results will extend the search for substrate supported QSH materials to new lattice and orbital types. |
Thursday, March 8, 2018 8:12AM - 8:24AM |
R17.00002: Quantized Berry Phase and Surface States in the Presence of Reflection or Space-Time Inversion Symmetry Andreas Schnyder, Ching-Kai Chiu, Yang-hao Chan Reflection symmetry or space-time inversion symmetry quantizes the Berry phase to 0 or \pi. This in turn can lead to the protection of nodal lines in systems with negligible spin-orbit coupling. In this work, we show that to prove the Berry phase quantization, it is most convenient to use the cell-periodic convention and to choose the coordinates such that the origin is at the reflectioin (inversion) center. In addition, we show that a \pi Berry phase is not a sufficient condition for the presence of stable surface states. Their presence crucially depends on the surface termination and the atom distribution in the unit cell. By using these new conditions we examine if stable surface states exist in known topological nodal line materials. |
Thursday, March 8, 2018 8:24AM - 8:36AM |
R17.00003: STM Study of Draped and Wrinkled Graphene Riju Banerjee, Lavish Pabbi, Bill Dusch, Anna Snelgrove, Tomotaroh Granzier-Nakajima, Mauricio Terrones, Eric Hudson
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Thursday, March 8, 2018 8:36AM - 8:48AM |
R17.00004: The electronic properties of graphene on SrTiO3 and Pt substrates Jinwoong Hwang, Hyejin Ryu, Hwihyeon Hwang, Min-Jeong Kim, Ji-Eun Lee, Qin Zhou, Debin Wang, Ankit Disa, Jonathan Denlinger, Yuegang Zhang, Alessandra Lanzara, Sung-Kwan Mo, Choongyu Hwang Interactions between two different materials sometimes provide a viable route towards the comprehension of intrinsic physical properties of each material and induce novel physical properties that do not exist in each material alone. We have investigated graphene on two different substrates, SrTiO3 and Pt, using angle-resolved photoemission spectroscopy. The electron band structure of graphene on SrTiO3 shows a deviation from the characteristic linearity that is not explained within the Fermi liquid theory. Such deviation is further enhanced with decreasing temperature revealing strong electron-electron interactions in graphene at low temperatures. Graphene on Pt also shows the characteristics of strong electron-electron interactions, despite the presence of Pt strongly influences the electronic properties of graphene. Our findings pave the way towards the possible realization of strong correlations between Dirac fermions in graphene. |
Thursday, March 8, 2018 8:48AM - 9:00AM |
R17.00005: Abstract Withdrawn
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Thursday, March 8, 2018 9:00AM - 9:12AM |
R17.00006: First-Principles Prediction of Giant 1D Rashba Splitting in Bismuth-adsorbed Atomic Nanowires Tomonori Tanaka, Yoshihiro Gohda We investigated that bismuth-adsorbed In/Si(111)–4×1 quasi one-dimensional surfaces, using first-principles calculations based on density functional theory. As a result, giant 1D Rashba splittings are observed due to the combination of In/Si(111) one–dimensionality and the spin–orbit coupling. Especially, a metastable surface of 1/4–monolayer bismuth coverage indicates the large out–of–plane spin polarization in Rahsba-split states. We have estimated the magnitude of the spin splitting by the linear approximation of the split width, and obtained the Rashba parameter, 1.8 eVÅ. This is one of the largest values in 1D the Rashba systems. |
Thursday, March 8, 2018 9:12AM - 9:24AM |
R17.00007: Chemical potential tuning and strain engineering in topological half-Heusler thin films Shouvik Chatterjee, John Logan, Nathaniel Wilson, Hadass Inbar, Tobias Brown-Heft, Alexei Fedorov, Chris Palmstrom Heusler compounds have emerged as an exciting material system where realization of functional and tunable novel topological phases might be possible. PtLuSb is one such compound that has recently been shown to host topologically non-trivial surface states. However, the chemical potential was found to lie below the Dirac point of the surface states, consistent with p-type Hall conductivity, in our thin films. One way to shift the chemical potential above the Dirac point is to substitute a few of the platinum (Pt) atoms in PtLuSb with gold (Au), which has one more electron compared to Pt. Employing a combination of the techniques of angle-resolved photoemission spectroscopy via a UHV vacuum suitcase transfer and in-situ scanning tunneling spectroscopy along with ex-situ transport measurements we will provide evidence of our ability to tune the chemical potential via substitution alloying in PtxAu1-xLuSb thin films, in particular, the Fermi Level can be shifted close to the Dirac point for 38% Au concentration. In this talk, I will also present our efforts to synthesize bi-axially strained thin films on lattice mismatched substrate in order to lift the degeneracy of the Γ8 manifold, thereby opening a bulk band gap in this otherwise semi-metallic compound. |
Thursday, March 8, 2018 9:24AM - 9:36AM |
R17.00008: Large-gap Quantum Spin Hall Insulators in Chemically Functionalized Bi(110) Bilayers Weidong Luo, Ping Li For applications of quantum spin Hall (QSH) insulators, the materials need to possess large energy gaps, and they should maintain their non-trivial topological properties when fabricated on substrates. Many QSH insulators have been theoretically proposed, but only a few of them have been experimentally confirmed. Based on first-principles calculations we find that the Bi(110) bilayer, which is metallic in its pristine form, can transform into QSH insulators through hydrogenation and halogenation. Their energy gaps are among the largest, ranging from 0.45 to 0.93 eV, for QSH insulators. A pz-σ bonding-antibonding splitting mechanism and a charge-transfer mechanism are proposed to understand their electronic structures. These topologically insulating films exhibit excellent dynamical and thermal stability, and could robustly maintain their topological properties against large strains and substrate effects. On MoSe2 and black phosphorus substrates, the functionalized Bi films form nearly freestanding QSH insulators and show large global energy gaps enough for room temperature utilizations. |
Thursday, March 8, 2018 9:36AM - 9:48AM |
R17.00009: Large-scale formation of ordered one-third-hydrogenated graphene on Ru(0001) De-Liang Bao, Hui Chen, Wende Xiao, Dongfei Wang, Yande Que, Kai Qian, Shuai Zhang, Hui Guo, Rong Yang, Guangyu Zhang, Yuyang Zhang, Jiatao Sun, Xiao Lin, Shixuan Du, Sokrates Pantelides, Hongjun Gao It is generally thought that hydrogen atoms can chemisorb on graphene in a perfect periodic manner, forming new crystalline two-dimensional (2D) materials that exhibit unique electronic properties beyond pristine graphene, such as graphane, graphone and 2D CxHy. So far, samples with small patches of ordered hydrogen adatoms can only be produced. Here, we present atomically resolved scanning tunneling microscope (STM) images that demonstrate the fabrication of one-third hydrogenated graphene that is perfectly ordered over hundreds of nanometers. Moreover, we show that, this crystalline one-third-hydrogenated graphene is decoupled from the substrate and structurally anisotropic. Calculations show that the structural anisotropy of one-third hydrogenation results in an anisotropic electronic structure. The present work directly provides atomic-scale evidence that new, large-scale 2D crystals with designed electronic properties can be realized by attaching other atoms and molecules onto graphene. |
Thursday, March 8, 2018 9:48AM - 10:00AM |
R17.00010: Exploring environment-dependent shape evolution in Bi2Se3 nano-crystallites: A first-principles thermodynamics approach Jiwoo Lee, Aloysius Soon Bismuth selenide (Bi2Se3) has attracted much interest and has found niche applications in various fields of thermoelectrics, topologically non-trivial systems, as well as in progressive radiotherapy medical treatments. Until recently, the solution-based solvothermal method has been shown to be a very promising way to achieve high scalability and crystallinity for cost-effective large-scale production. By carefully controlling the experimental conditions, the shape and size can be manipulated. However, there is still a lack of understanding regarding the underlying mechanism that governs the preferred shape growth where classical models (e.g. Lamer model) cannot provide a complete explanation. In this work, we perform first-principles calculations and model the environment-dependent shape evolution of Bi2Se3 nanocrystals with the Gibbs-Wulff theorem. Here, we examine how the various growth conditions (e.g. defects, precursor, solvent, etc.) can contribute to the thermodynamic shape evolution and predict/explain experimentally observed morphologies of Bi2Se3. |
Thursday, March 8, 2018 10:00AM - 10:12AM |
R17.00011: Temperature-dependent Raman Spectroscopy of Doped and Undoped Topological Insulators Pheona Williams, Yunbo Ou, Jeffrey Simpson, Angela Hight Walker, Prabhakar Misra, Joseph Checkelsky, Jagadeesh Moodera, Thomas Searles Topological insulators, materials whose bulk interior is insulating but have an unusual two dimensional electronic state at the surface, represent a new class of quantum materials now being intensively investigated. The objective of this work was to study how the introduction of magnetic dopants affect the Raman response of topological insulator thin films in terms of spectral peak position and linewidth. We performed temperature dependent Raman spectroscopy on 8nm thick doped and undoped samples of capped Bi2Te3 thin films grown by molecular beam epitaxy. The dopants used were Cr and V at 2% and 4% replacement of Bi. We describe the effect of this doping on the position, and full width at half maximum of the observed thin film spectra. From the analysis of the temperature dependent Raman response, we suggest that this behaviour can be understood in terms of doping-induced strain. This study revealed information about the lattice dynamical properties of Bi2Te3; in particular, how these properties evolve with the manipulation of metallic and transition metallic atoms in the topological insulator lattice. |
Thursday, March 8, 2018 10:12AM - 10:24AM |
R17.00012: Quasiparticle interference on Dirac nodal line semimetal ZrSiSe surface Hao Zheng, Jinfeng Jia The discovery of Dirac and Weyl semimetals opens a new era of research on topological non-trivial materials. In contrast to zero-dimensional nodal point inside theses material’s bulk band structure, the bands crossing forms novel line shaped nodes in the so-called nodal line semimetal. ZrSiX (X= S, Se, Te) was predicted and comfirmed by ARPES experiments as a Dirac nodal line material. In this talk, we will present the first quasiparticle interference experimental and theoretical results on ZrSiSe (001) surfaces by meaning of low temperature scanning tunneling microscopy and first principle simulation. The topological properties revealed by the data will also be discussed. |
Thursday, March 8, 2018 10:24AM - 10:36AM |
R17.00013: Ultrafast electron dynamics of Rashba-split 2-dimensional electron gas in topological insulators Matteo Michiardi, Fabio Boschini, Ryan Day, Pascal Nigge, Giorgio Levy, Marta Zonno, Elia Razzoli, Amy Qu, Sergey Zhdanovich, Michael Schneider, Bo Iversen, Philip Hofmann, Andrea Damascelli The study of 2 Dimensional Electron Gasses (2DEGs) at semiconductors interfaces dates back many decades, and today 2DEGs in field effect transistors are at the heart of modern electronics. It was recently discovered that 2DEGs can be induced on the surface of topological insulators (TI), leading to quantum well states with strong and exotic Rashba splitting [1-3]. The coexistence of spin polarized 2DEGs and topological states on the surface of TIs has important repercussions on the transport properties and on the realization of topological devices. Here we report on the ultrafast response of spin-polarized 2DEGs to optical excitation. Samples of bismuth chalcogenide TIs are chemically gated via adsorption of alkali metals on the surface, resulting in the formation of 2DEGs. Time-resolved ARPES is employed to study the ultrafast electron dynamics of the Rashba split 2DEGs as a function of spin-orbit coupling strength, doping level, and chemical composition. Our results give new insights in the physics of Rashba states and on their interplay with the topological state. |
Thursday, March 8, 2018 10:36AM - 10:48AM |
R17.00014: Induced Robust Topological Order on an Ordinary Insulator Heterostructured with a Strong Topological Insulator Bin LI, Qiangsheng Lu, Shuigang Xu, Xiangbin Cai, YIPU XIA, Wingkin Ho, Ning Wang, Hailang Qin, Gan Wang, Chang Liu, MAOHAI XIE Three of V(Bi, Sb)-VI(Se, Te) binary compounds are predicted and confirmed to be strong topological insulators (STIs). The exception for Sb2Se3 to be an ordinary insulator (OI) is due to the weaker spin-orbit coupling. Here, we report that the rhombohedral phase of Sb2Se3 is successfully grown by molecular beam epitaxy on films of Bi2Se3 (an STI) and In2Se3 (an OI). Surface electronic structures of these heterostructures are investigated by angle-resolved photoemission spectroscopy. In the OI/STI heterostructure, a Dirac cone topological surface state (TSS) is found to be induced on the Sb2Se3 layer up to 15 nm thick, in sharp contrast with the OI/OI heterostructure where no sign of TSS can be observed. |
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