Bulletin of the American Physical Society
APS March Meeting 2020
Volume 65, Number 1
Monday–Friday, March 2–6, 2020; Denver, Colorado
Session D39: First-principles modeling of excited-state phenomena in materials III: GW+BSE for Polarons and Optical ExcitationsFocus
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Sponsoring Units: DCOMP DMP DCP Chair: Sahar Sharifzadeh, Boston Univ Room: 703 |
Monday, March 2, 2020 2:30PM - 3:06PM |
D39.00001: Polarons from first principles Invited Speaker: Feliciano Giustino Polarons are among the most well-known quasiparticles in solid state physics, and are key to understanding fundamental concepts such as the electron mass enhancement in semiconductors and the formation of Cooper pairs in superconductors. Interest in polaron physics has been reignited by recent angle-resolved photoelectron spectroscopy studies, which revealed polaronic signatures in the band structures of several metal oxides and two-dimensional semiconductors. In this talk I will describe our recent work aimed at describing polarons and their spectroscopic signatures from first principles. In the first part of the talk I will outline a general many-body framework to compute and analyze polaron satellites in photoelectron spectra using the cumulant expansion approach [1,2]. I will discuss applications to titanium dioxide and europium oxide, and show that the calculations are able to reproduce very closely measured angle-resolved photoelectron spectra. In the second part of the talk I will address the question on how to compute the wavefunction of a polaron. I will describe a new approach to the polaron problem that overcomes some of the limitations of explicit supercell calculations [3]. This approach enables systematic calculations of wavefunctions and formation energies for both small and large polarons, and can be used to analyze the electron-phonon coupling mechanisms responsible for electron or hole self-trapping. I will illustrate these concepts using lithium fluoride and lithium oxide as examples, and I will discuss the connection with previous work on the polaron problem based on model Hamiltonians. |
Monday, March 2, 2020 3:06PM - 3:18PM |
D39.00002: Theory and First-Principle Calculation of Photoemission Spectra from Optically Excited States Ting Cao, Keshav M Dani, Tony F Heinz The behaviors of optically excited states, such as excitons, not only give rise to a variety of fascinating phenomena in condensed matter, but also play vital roles in modern optoelectronics and energy harvesting. In this talk, I will present our recent development on the theory and first-principle methods in the study of the photoemission spectra of low-dimensional materials. By performing calculations based on many-body perturbation theories, we show that, in monolayer transition metal dichalcogenides, the excitons hold unique energy dispersions and spectra weights in photoemission, which unveil the fundamental physical properties of these excited states. We further connect our theoretical works to experimental results and explore their potential applications in other systems. |
Monday, March 2, 2020 3:18PM - 3:30PM |
D39.00003: First Principles Studies of Photoluminescence of Functional Materials Yu Jin, Marco Govoni, Giulia Galli In order to predict the opto-electronic properties of several classes of functional materials, an accurate description of absorption and photoluminescence processes is necessary. Building on our previous work on calculations of absorption spectra from first principles [1], we present a method to compute photoluminescence spectra based on the solution of the generalized quantum Liouville equation, including electron-phonon interaction [2]. We present results for the photoluminescence spectra of organic/inorganic perovskites and of optically controllable defects in semiconductors. |
Monday, March 2, 2020 3:30PM - 3:42PM |
D39.00004: Deep ultraviolet luminescence and charge-transfer excitons in atomically thin GaN quantum wells Woncheol Lee, Dylan Bayerl, Nocona Sanders, Zihao Deng, Emmanouil Kioupakis We investigate the electronic, excitonic, and optical properties of atomically thin GaN quantum wells embedded in AlN or AlGaN barriers using first-principles calculations based on density functional theory (DFT) and many-body perturbation theory. The strong quantum confinement results in deep ultraviolet luminescence. Also, the quasi-2D structural characteristic produces strongly bound excitons, which are even stable at room temperature. We also investigate the properties of pairs of atomically thin GaN wells, separated by polar AlN barriers. The perpendicular electrical polarization produces charge-transfer excitons, in which electrons and holes are spatially separated in the two different GaN wells. Compared to direct excitons, the reduced overlap of charge-transfer excitons enables exciton lifetime that are 3-4 orders of magnitude longer. By adjusting the separation distance between electrons and holes through variations of the well and barrier thickness we can control the exciton lifetime and the binding energy simultaneously. |
Monday, March 2, 2020 3:42PM - 3:54PM |
D39.00005: Analysis of diagonal G and subspace W approximations within fully self-consistent GW calculations for bulk semiconducting systems Yashpal Singh, Lin-Wang Wang Fully self-consistent GW (sc-GW) methods are now available to evaluate quasiparticle and spectral properties of various molecular and bulk systems. However, such techniques are computationally demanding and act as a bottleneck to include vertex function. In contrast, routinely used single-shot G0W0 approximation has an undesirable dependency on the choice of xc-functional. In this work, we consider AlAs, AlP, GaP, and ZnS as our prototype systems to perform sc-GW calculations by expressing the full G matrix using a plane-wave basis set. To reduce the computational cost, we present a framework within our sc-GW scheme to consider diagonal G and subspace W approximations. We analyse our results obtained from the above techniques by comparing against our fully sc-GW calculations and other similar approaches including experiments. The sub 2% difference in the values of the bandgap obtained from fully sc-GW and subspace W methods shows an encouraging direction to incorporate vertex function that could potentially improve overestimated sc-GW bandgaps. |
Monday, March 2, 2020 3:54PM - 4:06PM |
D39.00006: Spin-wave dispersion of Cu2MnAl, Ni2MnSn, and Pd2MnSn based on quasi-particle self-consistent GW method Haruki Okumura, Kazunori Sato, Takao Kotani We calculated the spin-wave dispersion and the stiffness constants of three metallic ferromagnetic Heusler alloys: Cu2MnAl, Ni2MnSn, and Pd2MnSn. We determined the ground state by the quasi-particle self-consistent GW (QSGW) method. In conjunction with the Wannier function, we obtain transverse dynamical spin susceptibility based on linear response method. It is found that the ground states within the QSGW are reasonably calculated to reproduce spin-wave dispersion around Gamma point. In Cu2MnAl, the magnetic moment in QSGW agrees with the experiment, but stiffness constant is underestimated. In Ni2MnSn, the QSGW overestimates the moment, as seen in the itinerant ferromagnetic case as FCC Ni; however, the stiffness in QSGW agrees with the experiment. In Pd2MnSn, the QSGW reproduces the spin-wave throughout the Brillouin zone, and the stiffness is close to the experiments. This agreement is due to the reasonable exchange splitting of Mn 3d in accordance with the large screened Coulomb interaction in QSGW. |
Monday, March 2, 2020 4:06PM - 4:18PM |
D39.00007: Self-consistent GW method for solids: efficient implementation Andrey Kutepov An efficient implementation of the self-consistent GW method in the FlapwMBPT code (https://www.bnl.gov/cmpmsd/flapwmbpt/) is presented. It features the evaluation of the polarizability and the self-energy which scales only linearly with respect to the system size. The total computational time scaling measurements show it to be between linear and quadratic up to 72 atoms in silicon supercells. Application to such materials as CoSbS (24 atoms), supercells of La2CuO4 (up to 56 atoms), and SmB6 (7 atoms) illustrate the potential of the approach in computational material science. |
Monday, March 2, 2020 4:18PM - 4:30PM |
D39.00008: Systematic QSGW calculations on the electronic structure of rare-earth nitrides Kazunori Sato, Takao Kotani, Katsuhiro Suzuki Rare-earth (RE) based light emitting materials are distinguished for their narrow line width, small temperature dependence and insensitivity to the environment. These characteristic properties mostly come from localized nature of 4f-states. Therefore, for accurate prediction and design of RE related functional material, reasonable description of 4f-states is indispensable. |
Monday, March 2, 2020 4:30PM - 4:42PM |
D39.00009: Jigsaw Puzzle Orbitals for Electronic Structure Dimitar Pashov, Mark Schilfgaarde We present the jigsaw-puzzle orbitals (JPOs), a recently developed basis set for solving the one-particle Schrödinger equation with an optimally constructed minimal basis set. We illustrate some of its advantages with QSGW bandstructure calculations. A significant improvement in self-energy interpolation is observed as well as physically intuitive dependency of the band gap on the projection range. |
Monday, March 2, 2020 4:42PM - 4:54PM |
D39.00010: First-principles Studies of Tl activated Scintillator Phosphor Materials: Towards an understanding of the Scintillation mechanism Andrew Canning, Mauro Del Ben, Jaroslaw Glodo Tl doped halide scintillator phosphors are amongst the most commonly used gamma ray detector materials for medical imaging, high energy physics and nuclear materials detection applications (e.g. CsI:Tl, NaI:Tl). Even so the complete scintillation process in these materials is still poorly understood. In particular in recent years there has been great interest in co-doping these materials to try and improve their detection performance. We have performed first-principles studies based on GGA, hybrid functionals and the GW/BSE method in tandem with experiments to understand the scintillation mechanism in these materials and how it could be improved by co-doping. In particular we have looked at the Tl exciton optical emission states and energy transfer mechanisms from the gamma ray to the Tl. Recently there has also been interest in new Tl bulk scintillators such as TLYC (Tl2LiYCl6) which we have also studied. |
Monday, March 2, 2020 4:54PM - 5:06PM |
D39.00011: Excitation Pathways in Resonant Inelastic X-ray Scattering
from Many-Body Perturbation Theory Christian Vorwerk, Francesco Sottile, Claudia Draxl Resonant inelastic x-ray scattering (RIXS) spectroscopy is a powerful tool to unravel the nature of elementary excitations in a wide range of crystalline materials. In the RIXS process, a core electron is excited through the absorption of an x-ray photon. Subsequently, a valence electron fills the core hole via the emission of a x-ray photon. The final many-body state contains an excited electron and a valence hole. Through resonant x-ray absorption and emission, RIXS offers an elemental and orbital selective probe of the electronic valence excitations. In this talk, we present a novel many-body approach to RIXS. We use explicit many-body excited states in the optical and x-ray region, as obtained from full diagonalization of the Bethe-Salpeter equation in an all-electron framework, to obtain an expression for the RIXS cross section. The RIXS cross section is expressed in terms of pathways between intermediate many-body states containing a core hole, and final many-body states containing a valence hole. We apply our in-depth analysis to the RIXS spectra of the flour K edge of LiF and carbon K edge of diamond. Our results show that the excitation pathways determine the spectral shape of the emission, and the importance of electron-hole correlation in the spectra. |
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