Bulletin of the American Physical Society
APS March Meeting 2014
Volume 59, Number 1
Monday–Friday, March 3–7, 2014; Denver, Colorado
Session M43: Electronic Structures of Insulators and Superconductors |
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Sponsoring Units: DCMP Chair: Tai C. Chiang, University of Illinois at Urbana-Champaign Room: Mile High Ballroom 4B |
Wednesday, March 5, 2014 11:15AM - 11:27AM |
M43.00001: Stress induced tunable dielectric LiAsSe2 Fan Zheng, John Brehm, Steve Young, Andrew Rappe Tunable dielectric materials have many applications for the new electric devices. Traditionally, electric field is applied in order to tune the dielectric. We proposed a new material - LiAsSe2 (space group $Cc$) as the potential tunable dielectric material. First-principle calculations show that with applying stress along [100] and [010] direction, dielectric constant can be enlarged by around factor of 3 depending on the stress magnitude. With calculated electronic structure, optical dielectric and absorption spectrum also show very large magnitude difference before and after applying stress. This large difference comes from the structure change. By shrinking in these two directions, the original alternating bonds length between neighboring As and Se atomic chain become even bonds. The top of valence band and bottom of conduction bands tend to exclusively contain Se $p_z$ orbital and As $p_z$ orbital. As a result, inter-band transition between there bands gives much larger transition dipoles. DFT+$U$ method is used in order to correct self-interaction error, especially to As atoms. [Preview Abstract] |
Wednesday, March 5, 2014 11:27AM - 11:39AM |
M43.00002: Valence band study of Sm$_{0.1}$Ca$_{0.9-x}$Sr$_{\mathrm{x}}$MnO$_{3}$ using high resolution photoemission spectroscopy Manas Kumar Dalai, Biju Raja Sekhar, Deepnarayan Biswas, Sangeeta Thakur, Kalobaran Maiti, Tai-Chang Chiang, Christine Martin We have studied the valence band electronic structure of Sm$_{0.1}$Ca$_{\mathrm{0.9-x}}$Sr$_{\mathrm{x}}$MnO$_{3}$ (x $=$ 0, 0.1, 0.3 and 0.6) at various temperatures using high resolution photoemission spectroscopy (HRPES). The data were taken using a Scienta R4000 energy analyser and the resolution was set at 5 meV. The doping dependent studies of Sm$_{0.1}$Ca$_{\mathrm{0.9-x}}$Sr$_{\mathrm{x}}$MnO$_{3}$ at 50 K, 100 K and 295 K are quite interesting. The density of e$_{\mathrm{g}}$ states near the Fermi level decreases with Sr substitution at the Ca site at 50 K. Also the similar trend has been observed at 100 K. At 295 K the changes in the e$_{\mathrm{g}}$ states is quite different than the earlier temperatures where the intensity remains the same for x $=$ 0, 0.1 and 0.3 and then decreases for x $=$ 0.6. These changes in the density of states near the Fermi level will be explained by taking into account the structural, electrical and magnetic properties associated with this system. [Preview Abstract] |
Wednesday, March 5, 2014 11:39AM - 11:51AM |
M43.00003: Investigation of the Band Alignment at h-BN/SiX Dielectric Interfaces utilizing X-ray Photoemission Marc French, Sean King, Jeff Bielefeld, Joe Otto, Michelle Paquette, Anthon Caruso Due to a wide band gap ($\sim $ 6 eV), close lattice matching (\textless 2{\%}) and atomic planarity, hexagonal boron nitride (h-BN) is of interest as a potential substrate and gate dielectric in graphene channel transistor devices. A key property for the success of h-BN as a gate dielectric in such devices is its interfacial band alignment with graphene, the gate contact metallization and the surrounding insulating dielectric materials. In this regard, we have utilized x-ray photoelectron spectroscopy (XPS) to determine the Schottky barrier and valence band offsets present at the interfaces between plasma enhanced chemically vapor deposited amorphous h-BN:H and a variety of materials including graphene, Cu, SiO$_{\mathrm{2}}$, a-SiN$_{\mathrm{x}}$:H, a-SiC:H, and Si. We show that in many instances the valence and conduction band offsets are significant ($\ge $ 2 eV) and favorable for a variety of possible h-BN/graphene transistor devices. [Preview Abstract] |
Wednesday, March 5, 2014 11:51AM - 12:03PM |
M43.00004: Ab initio calculation of d-metal L-edge RIXS spectra using many-body quantum chemistry methods Nikolay Bogdanov, Valentina Bisogni, Jochen Geck, Liviu Hozoi, Jeroen van den Brink We designed a fully ab initio quantum chemistry scheme for the computation of both d-d excitation energies and intensities as measured by resonant inelastic x-ray scattering (RIXS) in d-electron systems. RIXS has recently emerged as a powerful tool to reliably probe the charge, spin, and orbital degrees of freedom of correlated electrons in solids [1,2]. As a first application we picked up Li$_2$CuO$_2$, a quasi-1D Cu 3$d^9$ oxide with a simple valence configuration in the intermediate state. We use embedded-cluster MCSCF and MRCI techniques [3], including scalar relativistic effects, spin-orbit coupling, and the valence orbital relaxation in the presence of the core hole. The transition matrix elements of the dipole operator are obtained by non-orthogonal configuration interaction. A careful analysis of the RIXS spectra is important for understanding the interplay between local distortions and longer-range lattice anisotropy and its effect on the d-level electronic structure [3,4] and magnetic interactions [4]. [1] L. Ament {\it et al.} Rev. Mod. Phys. {\bf 83}, 705 (2011); [2] J. Schlappa{\it et al.} Nature {\bf 485}, 82 (2012); [3] H.-Y. Huang {\it et al.} Phys. Rev. B {\bf 84}, 235125 (2011); [4] N.~A. Bogdanov {\it et al.} Phys. Rev. Lett. {\bf 110}, 127206 (2013). [Preview Abstract] |
Wednesday, March 5, 2014 12:03PM - 12:15PM |
M43.00005: The electronic structure of thorium halides predicted by HSE and GW Jason Ellis, Xiaodong Wen, Richard Martin Recently, there has been a significant experimental push to measuring the VUV nuclear excitation of $^{229}$Th using optical spectroscopy. Large band gap Thorium halides such as ThF$_{4}$ and Na$_{2}$ThF$_{6}$ have been suggested as candidate materials for studying this nuclear transition, as they are transparent to the relevant optical frequencies. In this work, we compare the many body GW approach, hybrid density functional theory, and local density approximation calculations of the electronic structure of these materials, as well as the rest of the binary thorium halides (ThX$_{4}$, X=Cl,Br,I). [Preview Abstract] |
Wednesday, March 5, 2014 12:15PM - 12:27PM |
M43.00006: The low temperature Fermi surface of IrTe2 probed by quantum oscillations. Samuel Blake, Amalia Coldea, Matthew Watson, Arjun Narayanan, Alix McCollam, Shigeru Kasahara, Takuya Yamashita, Daiki Watanabe, Takasada Shibauchi, Yuju Matsuda, Robert Schoonmaker The transition metal dichalcogenide IrTe2 undergoes a structural transition at 280K [1]; doping on the Ir site suppresses this transition and induces superconductivity with $T$c of about 3K [2]. The nature of the structural transition is possibly driven by charge disproportionation and the effect this has on the electronic structure of the superconducting state is not fully understood. We report a low temperature investigation of the Fermi surface of IrTe2 from quantum oscillations, using torque measurements performed in magnetic fields up to 33T and temperatures down to 0.3K. The observed extremal areas of the Fermi surface likely correspond to frequencies of a reconstructed Fermi surface, with light effective masses below 0.8me. The angular dependence of these frequencies across multiple crystals of IrTe2 suggests these materials are prone to domain formation upon cooling. We compare our measured Fermi surface with those predicted by electronic structure calculations, based upon the existing structural models, for both above and below the structural transition. This work was supported by EPSRC (UK) and partly by EuroMagnet (EU contract number 228043). [1] Matsumoto et al., J. Low Temp. Phys. 117, 1129 (1999) [2] Fang et al., Sci. Rep. 3, 1153 (2013) [Preview Abstract] |
Wednesday, March 5, 2014 12:27PM - 12:39PM |
M43.00007: Structural phase transition induced by van Hove singularity in 5$d$ transition metal compound IrTe$_{2}$ Tian Qian, Hu Miao, Zhijun Wang, Xuerong Liu, Xun Shi, Yaobo Huang, Peng Zhang, Nan Xu, Pierre Richard, Ming Shi, M.H. Upton, J.P. Hill, Gang Xu, Xi Dai, Zhong Fang, H.C. Lei, C. Petrovic, Aifang Fang, Nanlin Wang, Hong Ding Comprehensive studies of the electronic states of Ir 5$d$ and Te 5$p$ have been performed to elucidate the origin of the structural phase transition in IrTe$_{2}$ by combining angle-resolved photoemission spectroscopy and resonant inelastic X-ray scattering. While no considerable changes are observed in the configuration of the Ir 5$d$ electronic states across the transition, indicating that the Ir 5$d$ orbitals are not involved in the transition, we reveal a van Hove singularity at the Fermi level ($E_{\mathrm{F}})$ related to the Te $p_{\mathrm{x}}+p_{\mathrm{y}}$ orbitals, which is removed from $E_{\mathrm{F}}$ at low temperatures. The wavevector connecting the adjacent saddle points is consistent with the in-plane projection of the superstructure modulation wavevector. These results can be qualitatively understood with the Rice-Scott ``saddle-point'' mechanism, while effects of the lattice distortions need to be additionally involved. [Preview Abstract] |
Wednesday, March 5, 2014 12:39PM - 12:51PM |
M43.00008: Investigation of strain effects in the charge density waves of $2H$-NbSe$_2$ Kane Scipioni, Ilija Zeljkovic, Daniel Walkup, Yoshinori Okada, Wenwen Zhou, Vidya Madhavan The transition metal dichalcogenide $2H$-NbSe$_2$ possesses coexisting superconducting and charge density wave (CDW) ordered states, which possibly compete below the critical transition temperature, $\sim$7.2K. Previous studies of this system have seen that the CDW is very susceptible to alterations due to local strain. This suggests proximity to a quantum critical point. In this study, we use scanning tunneling microscopy and spectroscopy to investigate the intimate relationship between mechanical strain and the electronic properties of $2H$-NbSe$_2$, and observe the evolution of electronic states on atomic length scales. [Preview Abstract] |
Wednesday, March 5, 2014 12:51PM - 1:03PM |
M43.00009: Enhanced Electron Interactions on Hydrogen Adsorbed ZnO Surface Ryu Yukawa, Kenichi Ozawa, Susumu Yamamoto, Hideaki Iwasawa, Jian Jiang, Hirokazu Hayashi, Taiki Horike, Yorito Nagata, Kenya Shimada, Hirofumi Namatame, Masaki Taniguchi, Iwao Matsuda Zinc oxide (ZnO) is a wide band- gap semiconductor (3.37 eV), and is widely used as a catalyst, a chemical sensor, and a variety of electronic and photonic devices. Recent studies have revealed that a two-dimensional electron gas (2DEG) is formed on a hydrogen adsorbed ZnO(10$\bar{1}$0) surface. However, a precise structure of the 2DEG on a ZnO surface is still uncertain. We have investigated the electronic states using angle-resolved photoemission spectroscopy (ARPES), and found the clear incoherent states associated with the coherent metallic peaks near the Fermi-level, giving direct evidence of many-body interactions inherent to 2D metallic states. The incoherent states are enhanced by the hydrogen adsorptions. Thus, we suggest that the incoherent peaks are originated from electron-phonon and electron-electrons interactions enhanced by the electron doping on the surface. [Preview Abstract] |
Wednesday, March 5, 2014 1:03PM - 1:15PM |
M43.00010: Angle-Resolved Synchrotron Photoemission Spectroscopy and Density Functional Theory Studies on Iridium Modified Si(111) Surface Nuri Oncel, Deniz Cakir, J. Hugo Dil, Bartosz Slomski, Gabriel Landolt The physical and electronic properties of Ir modified Si(111) surface has been investigated with the help of Angle Resolved Photoemission Spectroscopy (ARPES) and Density Functional Theory (DFT). The surface consists of Ir-ring clusters that form $\sqrt 7 \times \sqrt 7 \,R\,19.1^{0}-Ir$ reconstruction. The band structure around the Fermi level is dominated by the projected bulk states and the states originating from the `1x1' domains of the underlying Si substrate. The dispersion of these states is heavily modified due to umklapp scattering from the surface Brillouion zone. The morphology of the surface and the origins of the observed electronic states are explored and confirmed by DFT calculations. [Preview Abstract] |
Wednesday, March 5, 2014 1:15PM - 1:27PM |
M43.00011: 3-dimensional electronic structures of CaC6 Wonshik Kyung, Yeongkwan Kim, Garam Han, Choonshik Leem, Junsung Kim, Yeongwook Kim, Keunsu Kim, Eli Rotenberg, Changyoung Kim There is still remaining issues on origin of superconductivity in graphite intercalation compounds, especially CaC6 because of its relatively high transition temperature than other GICs. There are two competing theories on where the superconductivity occurs in this material; intercalant metal or charge doped graphene layer. To elucidate this issue, it is necessary to confirm existence of intercalant driven band. Therefore, we performed 3 dimensional electronic structure studies with ARPES to find out 3d dispersive intercalant band. However, we could not observe it, instead observed 3d dispersive carbon band. This support the aspect of charge doped graphene superconductivity more than intercalant driving aspect. [Preview Abstract] |
Wednesday, March 5, 2014 1:27PM - 1:39PM |
M43.00012: Doping dependence of dispersion renormalizations in strongly correlated materials with electron-phonon coupling Beth Nowadnick, Steven Johnston, Brian Moritz, Richard Scalettar, Thomas Devereaux The renormalization of band dispersions by interactions provides insight into the underlying physics in a strongly correlated material. Coupling between electrons and bosons leads to dispersion kinks at the boson energy, while electronic interactions alone can lead to strong correlation kinks, which generally occur at a higher energy scale. Both of these types of kinks have been observed by ARPES in a variety of strongly correlated materials. Since dispersion kinks yield information on interaction strength, in a system with multiple strong interactions, it is important to disentangle the effects of these interactions on dispersion renormalizations. In order to gain insight into this issue, we simulate the single-band Hubbard-Holstein model using determinant quantum Monte Carlo, a numerically exact technique which allows the electron-electron and electron-phonon interactions to be treated on an equal footing. By analyzing the single particle spectral function for a variety of electron-electron and electron-phonon interaction strengths, we characterize how the interplay of these interactions influences the kink structure, and in particular, its evolution with hole and electron doping. [Preview Abstract] |
Wednesday, March 5, 2014 1:39PM - 1:51PM |
M43.00013: Real-time studies of the atomic layer deposition of metal oxides using Ambient pressure x-ray photoelectron spectroscopy Joachim Schnadt, Ashley R. Head, Shilpi Chaudhary, Sofie Yngman, Niclas Johansson, Olesia Snezhkova, Jan Knudsen, Jesper N. Andersen, Hendrik Bluhm, Anders Mikkelsen, Rainer Timm Performing atomic layer deposition (ALD) of metal oxides at pressures around 0.01 mbar slows the half reactions of the process to allow \textit{in situ} real-time probing of changes in the surface electronic structure using Ambient pressure x-ray photoelectron spectroscopy (APXPS). By monitoring the ALD process as it occurs, new details on the mechanisms of interface formation and thin film growth can be obtained. The deposition of HfO$_{2}$ on InAs and the deposition of TiO$_{2}$ on rutile titania from transition metal complexes and water were studied with APXPS. Predictable, cyclic chemical shifts of ligand and substrate ionizations are seen in the growth of the films, but the kinetics of the film growth differs for the two systems. Upon exposure to the titania surface, the titanium precursor reacts straightaway and gradually proceeds to completion. In contrast, the hafnium precursor does not interact with the surface immediately. Once an activation barrier is surpassed, the reaction occurs instantaneously. By understanding the reactivity of different precursors, the ALD process can be more easily optimized in applications that require thin films of metal oxides such as metal-oxide-semiconductor devices and catalytic surfaces. [Preview Abstract] |
Wednesday, March 5, 2014 1:51PM - 2:03PM |
M43.00014: The relative influence of many body and molecular motion effects for near-threshold N K x-ray emission spectra in ionic nitrogen insulating compounds T. Jach, J. Vinson, W.T. Elam, J. Denlinger Our previous studies of the factors affecting the N K x-ray emission spectra of ammonium chloride and ammonium nitrate have revealed the importance of many body effects and molecular motion at an excitation energy well above the K edge. Quasiparticle lifetimes of the valence bands and zero point motion of the molecular groups have proven to be unusually significant. Large changes are observed experimentally in the x-ray emission spectra of these compounds as the excitation energy is progressively lowered towards threshold. We compare experimental results with initial calculations of the spectra including excitonic effects, self-energy contributions, and molecular motion. [Preview Abstract] |
Wednesday, March 5, 2014 2:03PM - 2:15PM |
M43.00015: Effects of phonon broadening on x-ray near-edge spectra in molecular crystals John Vinson, Terrence Jach, Tim Elam, Jonathon Denlinger Calculations of near-edge x-ray spectra are often carried out using the average atomic coordinates from x-ray or neutron scattering experiments or from density functional theory (DFT) energy minimization. This neglects disorder from thermal and zero-point vibrations. Here we look at the nitrogen K-edge of ammonium chloride and ammonium nitrate, comparing Bethe-Salpeter calculations of absorption and fluorescence to experiment. We find that intra-molecular vibrational effects lead to significant, non-uniform broadening of the spectra, and that for some features zero-point motion is the primary source of the observed shape. [Preview Abstract] |
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