Bulletin of the American Physical Society
APS March Meeting 2016
Volume 61, Number 2
Monday–Friday, March 14–18, 2016; Baltimore, Maryland
Session P24: ManyBody Perturbation Theory for Electronic Excitations: Electronic StructureFocus

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Sponsoring Units: DMP Chair: Noa Marom, Tulane University Room: 323 
Wednesday, March 16, 2016 2:30PM  3:06PM 
P24.00001: Electronic structure from relativistic quasiparticle selfconsistent $GW$ calculations Invited Speaker: Stefan Bl\"ugel Most theoretical studies of topological insulators (TIs) are based on tightbinding descriptions and density functional theory (DFT). But recently, manybody calculations within the $GW$ approximation attract much attention in the study of these materials. We present an implementation of the quasiparticle selfconsistent (QS) $GW$ method where the spinorbit coupling (SOC) is fully taken into account in each iteration rather than added a posteriori. Within the allelectron FLAPW formalism, we show DFT, oneshot $GW$, and QS$GW$ calculations for several, wellknown TIs. We present a comparison of the calculations to photoemission spectroscopy and show that the $GW$ corrected bands agree much better with experiment. For example, we show that Bi$_2$Se$_3$ [1,2] is a direct gap semiconductor, in contrast to what was believed for many years by interpreting experimental results on the basis of DFT and that small strains in Bi can lead to a semimetaltosemiconductor or trivialtotopological transitions [3]. Quasiparticle calculations for lowdimensional systems are still very demanding. In order to study the topological surface states with an approach based on $GW$, we use Wannier functions to construct a Hamiltonian that reproduces the manybody band structure of the bulk, and that is used to construct a slab Hamiltonian. With this approach, we discuss the effect of quasiparticle corrections on the surface states of TIs and on the interaction between bulk and surface states. [1] I. Aguilera \textit{et al.}, PRB {\bf 88}, 045206 (2013), \textit{ibid}., PRB {\bf 88}, 165136 (2013). [2] M. Michiardi \textit{et al.}, PRB \textbf{90}, 075105 (2014). [3] I.\ Aguilera \textit{et al.}, PRB \textbf{91}, 125129 (2015). [Preview Abstract] 
Wednesday, March 16, 2016 3:06PM  3:18PM 
P24.00002: Quasiparticle electronic structure of Bi$_2$Se$_3$ via the scCOHSEX+GW approach Bradford A. Barker, Jack Deslippe, Oleg Yazyev, Steven G. Louie We present ab initio calculations of the quasiparticle electronic band structure of threedimensional topological insulator material Bi$_2$Se$_3$ using the full spinor GW approach. The meanfield is initially computed at the DFT level in the local density approximation (LDA) using fullyrelativistic pseudopotentials. We then improve the meanfield electronic structure by solving Dyson's equation in the static COHSEX approximation, selfconsistently updating the eigenvalues, eigenvectors, and dielectric screening. After a few iterations, we then perform a GW calculation to determine the quasiparticle energies. We compare our calculated results to experimental values of the band gaps and effective masses. [Preview Abstract] 
Wednesday, March 16, 2016 3:18PM  3:30PM 
P24.00003: Ubiquitous electronplasmon coupling in doped semiconductors Fabio Caruso, Feliciano Giustino The interplay between electrons and bosonic excitations [as, e.g., phonons, collective chargedensity fluctuations (plasmons), and magnons] is pervasive in matter and underlies an extremely broad spectrum of physical phenomena, as, for instance, current dissipation, superconductivity, hotcarrier thermalisation, and band structure replicas [1]. At variance with phonons, however, questions pertaining the strength of electronplasmon coupling in solids are still awaiting further investigations. We developed and implemented a firstprinciples theory of electronplasmon coupling based on manybody perturbation theory. Our firstprinciples calculations reveal that electronplasmon coupling alters ubiquitously the dynamical and optical properties of semiconductors at high doping concentrations. This behaviour stems from the emergence of lowenergy extrinsic plasmons which may couple electronic states in the vicinity of the Fermi energy. [1] F. Caruso, H. Lambert, and F. Giustino, Phys. Rev. Lett. {\bf 114}, 146404 (2015). [Preview Abstract] 
Wednesday, March 16, 2016 3:30PM  3:42PM 
P24.00004: Quasiparticle excitations of adsorbates on doped graphene Johannes Lischner, Sebastian Wickenburg, Dillon Wong, Christoph Karrasch, Yang Wang, Jiong Lu, Arash A. Omrani, Victor Brar, HsinZon Tsai, Qiong Wu, Fabiano Corsetti, Arash Mostofi, Roland K. Kawakami, Joel Moore, Alex Zettl, Steven G. Louie, Mike Crommie Adsorbed atoms and molecules can modify the electronic structure of graphene, but in turn it is also possible to control the properties of adsorbates via the graphene substrate. In my talk, I will discuss the electronic structure of F4TCNQ molecules on doped graphene and present a firstprinciples based theory of quasiparticle excitations that captures the interplay of dopingdependent image charge interactions between substrate and adsorbate and electronelectron interaction effects on the molecule. The resulting dopingdependent quasiparticle energies will be compared to experimental scanning tunnelling spectra. Finally, I will also discuss the effects of charged adsorbates on the electronic structure of doped graphene. [Preview Abstract] 
Wednesday, March 16, 2016 3:42PM  3:54PM 
P24.00005: First Principles Charge Transfer Excitations in Curved Aromatic Materials Laura Zoppi, Layla Martin Samos, Kim K. Baldridge Understanding excitation properties and charge transport phenomena of curved $\pi $conjugated materials is critical for a rational utilization of buckybowls as electrically active materials in solidstate devices. In this respect, the class of materials based on the smallest bowlshaped fullerene fragment, corannulene, C$_{20}$H$_{10}$, offers a unique possibility for building up scaffolds with a tunable spectrum of structural and electronic properties.[1] Here, GWBSE based approaches are applied to investigation and prediction of charge transfer excitations of C$_{20}$H$_{10}$ materials systems at functional interfaces, [13] with a special emphasis on design aspects of materials relevant in the experimental domain. Theoretical predictions together with experimental findings illustrate the possibility of integrating corannulene electronic functions in molecular devices. [1] L. Zoppi, L. MartinSamos, K. K. Baldridge, \textit{Acc. Chem. Res}., 47, 33103320 (2014) [2] L. Zoppi, L. MartinSamos, K. K. Baldridge\textit{, J. Am. Chem. Soc.} 133, 1400214009 (2011) [3] L. Zoppi, L. Martin Samos, K. K. Baldridge, \textit{Phys. Chem. Chem. Phys.} 17, 61146121 (2015) [Preview Abstract] 
Wednesday, March 16, 2016 3:54PM  4:06PM 
P24.00006: Electronic and optical excitations in building blocks of the metal organic framework MOF5 Bin Shi, Linda Hung, Taner Yildirim, Serdar Ogut Metal organic frameworks (MOFs) are a relatively new class of materials which are made of metaloxide clusters linked by organic bridging ligands. In recent years, MOFs have received considerable attention due to their widely tunable structural, chemical and physical properties. We investigate one of the well characterized MOFs, MOF5, whose framework consists of tetrahedral [Zn$_4$0]$^{6+}$ units linked by rigid arylcarboxylate ligands. We use manybody perturbation (GW$+$BSE) and timedependent DFT methods in real space to examine the electronic and optical excitations in the building blocks of MOF5, such as Zn$_4$O(COOH)$_6$, basic zinc acetate [Zn$_4$O(CH$_3$COO)$_6$], and tetranuclear zinc benzoate [Zn$_4$O(C$_6$H$_5$COO)$_6$]. The calculated spectra are compared with available experimental measurements and existing calculations to shed light on the controversy regarding the nature (metalligand versus ligandligand) of lowenergy electronic and optical excitations in MOF5. [Preview Abstract] 
Wednesday, March 16, 2016 4:06PM  4:18PM 
P24.00007: Energy level alignment at hybridized organicmetal interfaces from a GW projection approach Yifeng Chen, Isaac Tamblyn, Su Ying Quek Energy level alignments at organicmetal interfaces are of profound importance in numerous (opto)electronic applications. Standard density functional theory (DFT) calculations generally give incorrect energy level alignments and missing longrange polarization effects. Previous efforts to address this problem using the manyelectron GW method have focused on physisorbed systems where hybridization effects are insignificant. Here, we use stateoftheart GW methods to predict the level alignment at the amineAu interface, where molecular levels do hybridize with metallic states. This nontrivial hybridization implies that DFT result is a poor approximation to the quasiparticle states. However, we find that the selfenergy operator is approximately diagonal in the molecular basis, allowing us to use a projection approach to predict the level alignments. Our results indicate that the metallic substrate reduces the HOMOLUMO gap by 3.5~4.0 eV, depending on the molecular coverage/presence of Au adatoms. Our GW results are further compared with those of a simple image charge model that describes the level alignment in physisorbed systems. [Preview Abstract] 
Wednesday, March 16, 2016 4:18PM  4:30PM 
P24.00008: Nonequilibrium transport in the AndersonHolstein model with interfacial screening Enrico Perfetto, Gianluca Stefanucci Image charge effects in nanoscale junctions with strong electronphonon coupling open the way to unexplored physical scenarios. Here we present a comprehensive study of the transport properties of the AndersonHolstein model in the presence of dotlead repulsion. We propose an accurate manybody approach to deal with the simultaneous occurrence of the FranckCondon blockade and the screeninginduced enhancement of the polaron mobility. Remarkably, we find that a novel mechanism of negative differential conductance origins from the competition between the charge blocking due to the electronphonon interaction and the charge deblocking due to the image charges. An experimental setup to observe this phenomenon is discussed. References [1] E. Perfetto, G. Stefanucci and M. Cini, Phys. Rev. B 85, 165437 (2012). [2] E. Perfetto and G. Stefanucci, Phys. Rev. B 88, 245437 (2013). [3] E. Perfetto and G. Stefanucci, Journal of Computational Electronics 14, 352 (2015). [Preview Abstract] 
Wednesday, March 16, 2016 4:30PM  4:42PM 
P24.00009: Manybody effects and ultraviolet renormalization in threedimensional Dirac materials Robert Throckmorton, Johannes Hofmann, Edwin Barnes We develop a theory for electronelectron interactioninduced manybody effects in three dimensional (3D) Weyl or Dirac semimetals, including interaction corrections to the polarizability, electron selfenergy, and vertex function, up to second order in the effective fine structure constant of the Dirac material. These results are used to derive the higherorder ultraviolet renormalization of the Fermi velocity, effective coupling, and quasiparticle residue, revealing that the corrections to the renormalization group (RG) flows of both the velocity and coupling counteract the leadingorder tendencies of velocity enhancement and coupling suppression at low energies. This in turn leads to the emergence of a critical coupling above which the interaction strength grows with decreasing energy scale. In addition, we identify a range of coupling strengths below the critical point in which the Fermi velocity varies nonmonotonically as the lowenergy, noninteracting fixed point is approached. Furthermore, we find that while the higherorder correction to the flow of the coupling is generally small compared to the leading order, the corresponding correction to the velocity flow carries an additional factor of the Dirac cone flavor number relative to the leadingorder result. [Preview Abstract] 
Wednesday, March 16, 2016 4:42PM  4:54PM 
P24.00010: Electronelectron interactions in Dirac and Weyl semimetals: collective modes and stability of the ground state John Tolsma, Allan MacDonald Threedimensional Dirac and Weyl semimetals host linearly dispersive lowenergy electronic bands in the bulk, and exotic FermiArc states at the surface. Following theoretical proposals of candidate material classes [1,2], experimental observation of anomalous transport [3] and FermiArc surface states [4] have recently been reported. Using timedependent HartreeFock and renormalization group methods, we study collective mode dispersion and the influence of electronelectron interactions on the stability of the ground state. This work was supported by the DOE Division of Materials Sciences and Engineering under grant DEFG02ER45118. [1] Z. Wang et al., Phys. Rev. B. 88, 125427 (2013) [2] S.M. Huang et al., Nat. Comm. 6, 7373 (2015) [3] T. Liang et al., Nat. Mater. 14, 280 (2014) [4] S.Y. Xu et al., Science 347, 294 (2015) [Preview Abstract] 
Wednesday, March 16, 2016 4:54PM  5:06PM 
P24.00011: Firstprinciples DFT+GW study of oxygen doped CdTe Walter Orellana, Mauricio A. Flores, Eduardo Men\'endezProupin The role of oxygen doping in CdTe is addressed by firstprinciples calculations. Formation energies, charge transition levels and quasiparticle defect states are calculated within the DFT+GW formalism. The formation of a new defect is identified, the $(\text{O}_{\text{Te}}\text{Te}_\text{Cd})$ complex. This complex is energetically favored over both isovalent (O$_{\text{Te}}$) and interstitial oxygen (O$_{\text{i}}$). We find that incorporation of oxygen passivates the harmful deep energy levels derived from Te antisites, suggesting an improvement in the efficiency of CdTe based solar cells. Our calculations indicate that both (O$_{\text{Te}}$) and (O$_{\text{i}}$) have low formation energies. Moreover, $(\text{O}_{\text{Cd}})$ is only stable in the neutral charge state and undergoes a JahnTeller distortion. The (V$_{\text{Cd}}$O$_{\text{Te}}$) complex is found to be a shallow acceptor with a high formation energy. We also report an oxygenrelated interstitial defect, which plays a key role in the diffusion mechanism of oxygen in CdTe. [Preview Abstract] 
Wednesday, March 16, 2016 5:06PM  5:18PM 
P24.00012: Quasiparticle band structure of potassiumdoped fewlayer black phosphorus with GW approximation Hangyu Kim, Seung Su Baik, Hyoung Joon Choi We calculate the quasiparticle band structure of pristine and potassiumdoped black phosphorus (BP) by using the GW approximation. We obtain band gaps of pristine bulk and fewlayer BP and compare them with the result of the density functional calculations and experimental measurements. For potassiumdoped cases, we calculate the electronic band structure of potassiumdoped fewlayer BPs with various doping densities. We obtain the critical doping density for the bandgap closing, and the energyband dispersions when the band gap is inverted. We discuss Dirac semimetal properties of doped fewlayer BPs obtained by the GW approximation. This work was supported by NRF of Korea (Grant No. 20110018306) and KISTI supercomputing center (Project No. KSC2015C3039). [Preview Abstract] 
Wednesday, March 16, 2016 5:18PM  5:30PM 
P24.00013: Quasiparticle and optical band gaps of Sr$_{n+1}$Ti$_{n}$O$_{3n+1}$ from \textit{abinitio} manybody perturbation theory Sebastian E ReyesLillo, Tonatiuh Rangel, Fabien Bruneval, Jeffrey B Neaton The Ruddlesden Popper homologous series Sr$_{n+1}$Ti$_{n}$O$_{3n+1}$ provides a unique opportunity to study the effect of dimensionality and confinement on the band gap and absorption spectrum of the complex oxide SrTiO$_3$. In this work, we use manybody perturbation theory within the \textit{GW} approximation and the BetheSalpeter equation (BSE) approach to study the electronic and optical properties of Sr$_{n+1}$Ti$_{n}$O$_{3n+1}$. We find that our \textit{GW}/BSE direct and indirect band gaps are in excellent agreement with measured direct and indirect optical gaps. We discuss technical aspects of the calculations such as convergence and startingpoint dependence, and compare to higher levels of theory. In addition, we find a relatively large exciton binding energy of 500 meV for Sr$_2$TiO$_4$ ($n=1$). We explore the role of structural distortions and epitaxial strain in the properties of the localized exciton. Our work suggests that layered structures can provide a viable route for the design of complex oxide materials with desirable optoelectronic properties. This work is supported by DOE. [Preview Abstract] 
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