Bulletin of the American Physical Society
APS March Meeting 2015
Volume 60, Number 1
Monday–Friday, March 2–6, 2015; San Antonio, Texas
Session Z7: Insulators: ARPES and Other Spectroscopies |
Hide Abstracts |
Sponsoring Units: DCMP Chair: Jonathan Denlinger, Lawrence Berkeley National Laboratory Room: 006B |
Friday, March 6, 2015 11:15AM - 11:27AM |
Z7.00001: Electronic structure origins of the extremely large magnetoresistance in tungsten ditelluride Ivo Pletikosic, Mazhar Ali, Robert Cava, Tonica Valla WTe$_2$ is a layered transition metal dichalcogenide showing a structural reduction to one-dimensional tellurium-surrounded tungsten chains. The material exhibits an extremely large positive anisotropic magnetoresistance of a few million percent that increases as the square of the field and shows no saturation up to 60 T. We explored the possible electronic structure origins of the magnetoresistance by means of angle-resolved photoelectron spectroscopy (ARPES) and found electron and hole pockets of equal size along the direction of tungsten chains, forming a highly anisotropic quasi-twodimensional Fermi surface. The perfect carrier compensation at low temperatures has been identified as the primary source of the magnetoresistive effect, and the change of the Fermi surface shape as well as a high-density-of-states band slightly below the Fermi level recognized as the cause of its diminishing at rising temperatures. [1] M.N. Ali et al. Nature 514, 205 (2014) [2] I. Pletikosi? et al. arXiv:1407.3576 (2014) [Preview Abstract] |
Friday, March 6, 2015 11:27AM - 11:39AM |
Z7.00002: Near Gap Excitation of Collective Modes in a Charge Density Wave Dominik Leuenberger, Jonathan Sobota, Shuolong Yang, Alexander Kemper, Paula Giraldo, Rob Moore, Ian Fisher, Patrick Kirchmann, Thomas Devereaux, Zhi-Xun Shen We present time- and angle-resolved photoemission spectroscopy (trARPES) measurements on the charge density wave system's (CDW) CeTe$_{3}$. Optical excitation transiently populates the unoccupied band structure and reveals a CDW gap size of $2\Delta =0.59$~eV. In addition, the occupied Te-$5p$ band dispersion is coherently modified by three collective modes. First, the spatial polarization of the modes is analyzed by fits of a transient model dispersion and DFT frozen phonon calculations. We thereby demonstrate how the rich information from trARPES allows identification of collective modes and their spatial polarization, which explains the mode-dependent coupling to charge order. Second, the exciting photon energy $h\nu$ was gradually lowered towards $2\Delta$, at constant optical excitation density. The coherent response of the amplitude mode deviates from the optical conductivity, which is dominated by direct interband transitions between the lower and upper CDW bands. The measured $h\nu$-dependence can be reproduced by a calculated joint density of states for optical transition between bands with different orbital character. This finding suggests, that the coherent response of the CDW amplitude mode is dominated by photo-doping of the charge ordering located in the Te-planes. [Preview Abstract] |
Friday, March 6, 2015 11:39AM - 11:51AM |
Z7.00003: Calculations of Photoemission from Rutile Harold Hjalmarson, Peter Schultz, Chris Moore Photoemission is a well-known mechanism for release of electrons from a surface during electrical breakdown of a gas such as air. During air breakdown, UV photons, which are emitted from the highly excited gas molecules, are absorbed in the surfaces such as the cathode and the anode. These absorbed photons create energetic electrons, and a small portion of these electrons reach the surface. Those that overcome the potential energy barrier at the surface tend to be emitted. In this talk, the Boltzmann equation that describes these phenomena is formulated. A Monte Carlo probabilistic method is used to obtain the rate of electron emission as a function of photon energy. The role of bandstructure effects will be discussed. This bandstructure information is obtained by using a density-functional theory (DFT) method. Sandia National Laboratories is a multi-program laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the U.S. Department of Energy's National Nuclear Security Administration under contract DE-AC04-94AL85000. [Preview Abstract] |
Friday, March 6, 2015 11:51AM - 12:03PM |
Z7.00004: Probing the Reversible Changes in Electronic Structure Induced by Liquid Electrolyte Gating in WO$_{3}$ Thin Films by Hard X-ray Photoelectron Spectroscopy Julie Karel, Carlos Viol Barbosa, Simone Altendorf, Janos Kiss, Yuki Utsumi, Mahesh Samant, Liu Hao Tjeng, Claudia Felser, Stuart Parkin Tungsten trioxide (WO$_{3})$ is a $d^{0}$ transition metal oxide that has attracted broad interest from both application and fundamental materials physics standpoints. It has been studied for use in photoelectrochemical hydrogen generation, smart windows, gas sensors and has been shown to exhibit high temperature surface superconductivity when doped with K or Cs. Many of these studies necessitate modifications in the carrier concentration and in particular oxygen deficiencies. In this work, we utilize liquid electrolyte gating to create oxygen vacancies in WO$_{3}$ thin films, a process we will show is reversible. The modifications in the electronic structure (core levels and valance band) resulting from the gating are probed by hard X-ray photoelectron spectroscopy. Electrolyte gating leads to a significant population of W 5d states in the conduction band and an enormous change in the W 4f core levels. \textit{Ab initio} density functional theory is used to help describe the origin of these modifications in the electronic structure. [Preview Abstract] |
Friday, March 6, 2015 12:03PM - 12:15PM |
Z7.00005: Angle resolved photoemission spectroscopy study on the non-saturate magnetoresistance material WTe$_{2}$ Juan Jiang, Xiaohai Niu, Binping Xie, Tong Zhang, Donglai Feng By performing high resolution angle-resolved photoemission spectroscopy, we obtain the detailed electronic structure of WTe$_{2}$, which has an extremely large non-saturated magnetoresistance. Unlike the simple one electron and one hole pocket as expected, we resolved a rather complicated Fermi surface in WTe$_{2}$. There is a hole pocket around the Brillouin zone center $\Gamma$, two hole pockets and two electron pockets along the tungsten chain direction. Thus the large magnetoresistance cannot be simply attributed to the electron-hole compensation, since this is based on a two carrier assumption model, the real case in WTe$_{2}$ should be more complicated. Surprisingly, the circular dichroism ARPES result shows a strong intensity inversion between the data under the right-circular polarized light and the left-circular polarized light. This, indicates a proper different orbital angular momentum along the tungsten chain direction, which might also related to the different spin angular momentum since there're coupled with each other. Therefore, we propose that to fully understand the large magnetoresistance in WTe$_{2}$, spin channel should also be involved where backscattering are forbidden under zero field. [Preview Abstract] |
Friday, March 6, 2015 12:15PM - 12:27PM |
Z7.00006: ARPES Study on Layer-Dependent Electronic Structure of FeSe/SrTiO3 Films Defa Liu, Lin Zhao, Xu Liu, Shaolong He, Yong Hu, Junfeng He, Wenhao Zhang, Fangsen Li, Chenjia Tang, Zhi Li, Lili Wang, Guodong Liu, Jun Zhang, Chuangtian Chen, Zuyan Xu, Xi Chen, Xucun Ma, Qikun Xue, Xingjiang Zhou the recent discover of high-Tc superconductivity in a single-layer FeSe/SrTiO3 film has attracted much attention.. Our previous ARPES studies on the FeSe/SrTiO3 films have observeddistinct electronic structure of the single-layer FeSe/SrTiO3 film, established a phase diagram and observed a signature of high Tc over 65K in the annealed single-layer FeSe/SrTiO3 films, revealed thedichotomy of electronic structure and superconductivity between the single-layer and double-layer FeSe/SrTiO3 films, and observed an insulator-superconductor transition in the single-layer FeSe/SrTiO3 films. In this talk, we will present our new ARPES results on the FeSe/SrTiO3 films with many different layers, from single-layer up to 50-layers. This systematic study will provide insight in understanding the evolution of electronic structure and superconductivity from the single-layer FeSe film, to multiple-layer FeSe film and eventually to the bulk FeSe superconductor. [Preview Abstract] |
Friday, March 6, 2015 12:27PM - 12:39PM |
Z7.00007: Angle Resolved Photoemission Study of Surface States and Orbital Angular Momentum Structure in SrTiO$_{3}$ Shoresh Soltani, Beomyoung Kim, Garam Han, Soohyun Cho, Jonathan Denlinger, Mats Leandersson, Changyoung Kim The theoretical understanding of spin orbit coupling (SOC) effects in SrTiO$_{3}$ (STO) and KTaO$_{3}$ (KTO) is still in its infancy. To have a better understanding of these effects, we have performed linear and circular dichroism angle resolved photoemission spectroscopy (LD- and CD-ARPES) of surface states of STO and KTO to measure the energy band and local orbital angular momentum (OAM) structure. CD-ARPES measurement revels the OAM chiral structure. Using ARPES results and a new OAM based Hamiltonian we try to explain the origin of band splitting. We believe that OAM has an important role in the surface band splitting and the chiral structure reveled by CD-ARPES. [Preview Abstract] |
Friday, March 6, 2015 12:39PM - 12:51PM |
Z7.00008: Electronic Structure of Silicene Studied by Angle Resolved Photoemission Spectroscopy Lin Zhao, Ya Feng, Zhuojin Xie, Baojie Feng, Xu Liu, Defa Liu, Kehui Wu, Shaolong He, Guodong Liu, Li Yu, Chuangtian Chen, Zuyan Xu, Xingjiang Zhou Silicene, similar to its counterpart of graphene, has generated a great interest. We have prepared silicenes on Ag(111) substrate and carried out angle resolved photoemission spectroscopy measurements on them. We will report on the electronic structure of silicene with different reconstruction configurations and discuss its implications. [Preview Abstract] |
(Author Not Attending)
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Z7.00009: kz Dependent Electronic Structure Studies of CaC6 and Inter Layer State Driven Superconductivity Wonshik Kyung, Yeongkwan Kim, Garam Han, Choonshik Leem, Chul Kim, Yoonyoung Koh, Beomyoung Kim, Yeongwook Kim, Junsung Kim, Keunsu Kim, Eli Rotenberg, Jonathan Denlinger, Changyoung Kim We performed angle-resolved photoemission experiments on CaC6 and measured kz dependent electronic structures to investigate the interlayer states. The results reveal a spherical interlayer Fermi surface centered at the $\Gamma $ point. We also find the graphene driven band possesses a weak kz dispersion. The overall electronic structure shows a peculiar single graphene layer periodicity in the kz direction although CaC6 unit cell is supposed to contain three graphene layers. This suggests that c-axis ordering of Ca has little effect on the electronic structure of CaC6. In addition to CaC6, we also studied the non-superconducting BaC6. For BaC6, the graphene band Dirac point energy is smaller than that of CaC6. Based on data from CaC6 and BaC6, we rule out Cxy phonon mode as the origin of the superconductivity in CaC6, which strongly suggests interlayer state driven supercondutivity. [Preview Abstract] |
Friday, March 6, 2015 1:03PM - 1:15PM |
Z7.00010: ABSTRACT WITHDRAWN |
Friday, March 6, 2015 1:15PM - 1:27PM |
Z7.00011: Direct Observation of the Bandwidth Control Mott Transition in the NiS$_{2-x}$Se$_x$ Multiband System H.C. Xu, Y. Zhang, M. Xu, R. Peng, X.P. Shen, V.N. Strocov, M. Shi, M. Kobayashi, T. Schmitt, B.P. Xie*, D.L. Feng* The bulk electronic structure of NiS$_{2-x}$Se$_x$ has been studied across the bandwidth-control Mott transition (BCMT) using soft x-ray angle-resolved photoemission spectroscopy. We show that Se doping does not alter the Fermi surface volume. When approaching the insulating phase with decreasing Se concentration, we observed that the Fermi velocity continuously decreases. Meanwhile, the weight of the coherent quasiparticle, which sits on a large incoherent spectrum, continuously decreases and is transferred to higher binding energies, until it suddenly disappears across the Mott transition. In the insulating phase, there is still finite spectral weight at the Fermi energy, but it is incoherent and dispersionless due to strong correlations. Our results provide a direct observation of the distinct characters of BCMT in a multiband non-half-filled system. [Preview Abstract] |
Friday, March 6, 2015 1:27PM - 1:39PM |
Z7.00012: Spatial crystal imaging by means of atomic electron holography Tobias Luehr, Aimo Winkelmann, Gert Nolze, Carsten Westphal The determination of atom structures is the key for the understanding of basic functional properties of matter or for designing new high-tech materials. For structure determination, holography is a very attractive option, since this method enables lensless three-dimensional imaging. In principle, x-ray photoelectron diffraction (XPD) experiments correspond to a microscopic holography setup. The electron diffraction pattern is highly sensitive to the local structure of the emitter environment, since the emitting atom is located in the near-field of the scattering atoms. Hence, holographic reconstructions of XPD-patterns should yield a spatial image of the sample's atom arrangement. However, anisotropic electron scattering and multiple scattering effects generally cause strong artifacts in the reconstruction. In this contribution we show how to circumvent this problem with electrons at kinetic energies of $E_{kin} \geq 10$ keV. The resulting spatial images contain hundreds of clearly separated atoms at their correct locations. Furthermore, XPD-patterns allow an element-specific assignment of the reconstructed atoms within the image. This is the first demonstration of true atom imaging following Dennis Gabor's idea of electron holography. [Preview Abstract] |
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