Bulletin of the American Physical Society
APS March Meeting 2021
Volume 66, Number 1
Monday–Friday, March 15–19, 2021; Virtual; Time Zone: Central Daylight Time, USA
Session F59: Electronic Structure: Theory and SpectraLive
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Sponsoring Units: FIAP Chair: Peihong Zhang, State Univ of NY - Buffalo |
Tuesday, March 16, 2021 11:30AM - 11:42AM Live |
F59.00001: Density-Matrix Theory with Renormalized Electron-Laser Coupling for Quantum-Dot Nonlinear Optical Response Danhong Huang, Xuejun Lu, Shanhui Fan A density-matrix theory has been employed for studying coherent electron dynamics in time-dependent occupation factors and induced quantum coherence for single and double quantum dots coupled to two incident laser fields. By introducing a self-consistent dynamical depolarization field, the renormalized light-electron interaction can be taken into account in connection with a quantum-mechanical exchange interaction between a pair of electrons within the same quantum dot. Moreover, the exchange interaction for two electrons in different quantum dots is also considered by applying the evanescent-field coupling based on a surface-plasmon model. In particular, the effect of quantum interference between two successively field-induced quantum coherences with respect to two lower and upper electronic states in a three-level quantum-dot system has been demonstrated, giving rise to a nonlinear optical response from indirect electron transition between the bottom and top energy levels. |
Tuesday, March 16, 2021 11:42AM - 11:54AM Live |
F59.00002: Spin-orbit coupling in wurtzite quantum wells Poliana Penteado, Jiyong Fu, Denis R Candido, Gerson J. Ferreira, Diego P. Pires, Esmerindo Bernardes, Carlos Egues In this work, we derive an effective spin-orbit Hamiltonian for conduction electrons valid for quantum wells, wires, and dots with arbitrary confining potentials and external magnetic fields. |
Tuesday, March 16, 2021 11:54AM - 12:06PM Live |
F59.00003: First-Principles Study of Microscopic Mechanism of High Ductility of Silver Sulfide/Selenide Hinata Hokyo, Masaaki Misawa, Shogo Fukushima, Kohei Shimamura, Akihide Koura, Fuyuki Shimojo Silver sulfide (Ag2S) is one of the important inorganic semiconductors for industrial use because it has metal-like ductility at room temperature. On the other hand, silver selenide (Ag2Se) does not show ductility, but has high electrical conductivity suitable for thermoelectric materials. By mixing these two chalcogenides, the development of flexible and high-performance semiconductors is expected. Experimental studies have reported that the ductility of Ag2S1-xSex mixtures is confirmed up to x = 0.6 with monoclinic Ag2S-type structure. In order to investigate the effects of Se addition on ductility of Ag2S, we performed simple shear deformation simulations of Ag2S1-xSex (x = 0, 0.2, 0.4, and 0.6) based on first-principles molecular dynamics method. Our simulations demonstrated that Ag2S1-xSex (x ≦ 0.6) systems have similar ductility properties to Ag2S. Additionally, we found that the high ductility is due to the structural recovery processes occurring in the following four mechanisms: 1) spontaneous sliding of the anion-sublattice, 2) interlayer/intralayer site exchange in the anion-sublattice, 3) self-healing of fracture parts of the anion-sublattice, and 4) splitting of lines of anions into two. |
Tuesday, March 16, 2021 12:06PM - 12:18PM Live |
F59.00004: Real space formulation for the electronic structure of randomly disordered quaternary semiconductor alloys applied on two dimensional (C2)x(BN)1-x Sujoy Datta Though the experimental work on random semiconductor alloys is prolific, theoretical investigations are limited. This is because of mainly two reasons, firstly, the orthodox density functional approximations often underestimate the band gaps of semiconductors, and secondly, a randomly alloyed structure with some concentration ratio of constituents may produce a lot of different configurations in reality and the necessary configuration averaging is always challenging for theorists. The advanced localized basis set of full potential N-th order muffin tin orbital (FP-NMTO) together with the improved exchange proposed by vanLeeuwen-Baerends (vLB) can predict the electronic properties of various semiconductors almost exactly. We extract the tight-binding parameters from the vLB-FP-NMTO first. Then, real-space Green functional method within augmented space formalism [J. Phys. C 6 1340 (1973)] which can perform configurational averaging on all possible arrangements by a tricky and fast mathematical formulation is utilized to propose an elegant method of calculating the electronic properties of semiconductor alloys, especially, the quaternary alloys with a preference towards the formation of particular bonds. We further exemplify this method on two-dimensional random (C2)x(BN)1-x alloy. |
Tuesday, March 16, 2021 12:18PM - 12:30PM Live |
F59.00005: Many Body Theory of Exciton and Trions in 2D Materials: Exciton-Trion Supersposition States and Exciton-Polarons Farhan Rana, Okan Koksal, Minwoo Jung, Christina Manolatou, Gennady Shvets The optical spectra of doped two-dimensional (2D) materials exhibit two sharp absorption peaks that are identified with excitons and trions. Many features of the measured spectra, such as the doping dependence of the energy separation and the spectral weights of these two peaks, cannot be explained by conventional models that treat excitons and trions as independent excitations. We show that in doped 2D materials, exciton and trions are strongly coupled as a result of Coulomb interactions and the resulting approximate eigenstates are exciton-trion supersposition states and correspond to the two peaks seen experimentally in the absorption spectra [1]. These eigenstates can be described by two coupled 2-body and 4-body Schrodinger equations. Solutions of these two coupled equations resemble variational exciton-polaron states [1] thereby establishing the relationship between our approach and Fermi polaron physics [2]. Our model can quantitatively explain all experimental results, including the observation of coherence in exciton-trion states and exciton-trion-polaritons in 2D materials. [1] Phys. Rev. B 102, 085304 (2020). [2] Nat. Phys. 13, 255 (2016). |
Tuesday, March 16, 2021 12:30PM - 12:42PM Live |
F59.00006: Electronic structure of semiconductor nanoparticles from stochastic evaluation of imaginary-time path integral Andrei Kryjevski The fermion sign problem, when severe, prevents the computation of physical quantities of a system of interacting fermions via stochastic evaluation of its path integral due to the oscillatory nature of the integrand exp(-S), where S is the imaginary-time action. However, in the Kohn-Sham orbital basis, which is the output of a Density Functional Theory simulation, the path integral for electrons in a semiconductor nanoparticle has only a mild fermion sign problem and is amenable to evaluation by standard stochastic methods. This is evidenced by our simulations of silicon hydrogen-passivated nanocrystals, such as Si35H36, Si87H76, Si147H100 and Si293H172, which range in size 1.0 - 2.4 nm and contain 176 to 1344 valence electrons. We find that approximating the fermion action by its leading order polarization term results in a positive-definite integrand, and is a very good approximation of the full action. We compute imaginary-time electron propagators and extract the energies of low-lying electron and hole levels. Our quasiparticle gap predictions agree with the results of previous high-precision G0W0 calculations. This formalism allows calculations of more complex excited states, such as excitons and trions. |
Tuesday, March 16, 2021 12:42PM - 12:54PM Live |
F59.00007: Long-distance coupling and energy transfer between exciton states in magnetically controlled microcavities Jan Suffczynski, Maciej Sciesiek, Krzysztof Sawicki, Wojciech Pacuski, Kamil Sobczak, Tomasz Kazimierczuk, Andrzej Golnik Realization of the strong coupling and energy transfer between spatially separated, and selectively addressable, semiconductor quantum emitters is essential for practical implementation of quantum information technology protocols. Here, we design and fabricate epitaxially a structure comprising two (Cd,Zn)Te based microcavities separated by over 2 µm and coupled through a semitransparent Bragg mirror.[1] Coupling of the emitter to the mode of one of the microcavities enables its interaction with a distant emitter coupled to mode of the other microcavity. A non-magnetic quantum well (QW) and mangetic, Mn-doped quantum well (MQW) is placed in the top and bottom microcavity, respectively. The magneto-photoluminescence measurements performed at T = 2 K demonstrate anticrossing of the polariton states for which a dominant contribution comes from QW and MQW excitons. Emission intensity dependences confirm energy transfer between the exciton states over the unprecedented distance of 2.1 µm. Control over the direction of the transfer is achieved by tuning of the exciton energy in MQW below or above the exciton in the QW using magnetic field.[1] |
Tuesday, March 16, 2021 12:54PM - 1:06PM Live |
F59.00008: Revealing the true bulk As-antisite defect in GaAs(110) using DFT calculations and STM/STS measurements Mary Clare Escano, Maria Herminia Balgos, Tien Quang Nguyen, Elizabeth Ann Prieto, Elmer Estacio, Arnel Salvador, Armando Somintac, Rafael Jaculbia, Norihiko Hayazawa, Yousoo Kim, Masahiko Tani Understanding mid-gap states in bulk semiconductors has profound implications in electronic/optoelectronic device design. For instance, mid-gap state from As-antisite defect (AsGa) is found to mediate below-band gap excitation at ~1560 nm (or 0.8 eV) [1,2]. Identifying and directly probing point defects in a semiconducting surface are thus important yet challenging. In this work, we were able to obtain the atomic and electronic characteristics of AsGa in GaAs(110) akin to bulk-AsGa using DFT calculations and STM/STS spectra. We found that the mid-gap state induced by AsGa in bulk GaAs is well-reproduced by the AsGa in the third layer of GaAs(110) [3]. We also found that the geometry and partial charge density of this defect mimics that of the bulk. Simulated and experimental STM images show an “asymmetric two-lobe” feature in the region around the defect. Using local density of states and STS spectra, we propose three peaks of characteristic energy levels corresponding to AsGa. These results constitute the first report of surface electronic signatures of true bulk point defect close to the surface of GaAs(110). |
Tuesday, March 16, 2021 1:06PM - 1:18PM Live |
F59.00009: First principle investigation of electronic, transport, and bulk properties of zinc-blende magnesium sulfide (MgS) Uttam Bhandari, Blaise Awola Ayirizia, Yuriy Malozovsky, Lashounda Franklin, Diola Bagayoko We have studied the electronic, structural, and transport properties of the zinc-blende magnesium sulfide (zb-MgS), using Density Functional Theory (DFT). We employed a Local Density Approximation (LDA) potential and the Linear Combination of Atomic Orbitals (LCAO) method. Our computational method leads to the ground state of materials without utilizing over-complete basis sets. The calculated direct band gap of zb-MgS is 4.43 eV, in excellent agreement with the experimental band gap of 4.45 ± 0.2 eV. We also report the total (DOS) and partial densities of states (pDOS), electron and holes effective masses, the equilibrium lattice constant, and the bulk modulus. |
Tuesday, March 16, 2021 1:18PM - 1:30PM Live |
F59.00010: Quasiparticle band structure for SrTiO3 and BaTiO3: A combined G0W0 and LDA+U approach Gabe Lopez-Candales, Zhao Tang, Weiyi Xia, Peihong Zhang We present the quasiparticle band structures of SrTiO3 and BaTiO3, two seemingly simple oxides. Previous G0W0 calculations predicted a band gap around 3.36 to 3.82 eV for SrTiO3 compared to the experimental value of 3.25 eV. A similar discrepancy between theory and experiment for BaTiO3 is observed. We show that the fully-converged G0W0 approach predicts reasonably accurate band gap values for both materials, provided that the calculations are carried out on top of LDA+U solutions. These results emphasize the deficiency of the LDA in describing the localized 3d states, in particular as a mean-field starting point for subsequent many-body perturbation calculations. This work demonstrates the accuracy and applicability of the combined G0W0 and LDA+U approach in calculating the quasiparticle band structures for materials involving localized 3d states, not only for systems with fully occupied 3d semicore states but also for 3d states which are unoccupied. |
Tuesday, March 16, 2021 1:30PM - 1:42PM Live |
F59.00011: Physics of the indirect- to direct-gap transition in group-IV semiconductor alloys Christopher Broderick, Eoin O'Reilly Development of CMOS-compatible photonic devices as a Si photonics enabling technology has stimulated efforts to engineer direct-gap group-IV semiconductors. Demonstrated lasing in Ge1-xSnx alloys has driven strong interest, and prompted investigations of Ge1-xCx and Ge1-xPbx alloys. |
Tuesday, March 16, 2021 1:42PM - 1:54PM Not Participating |
F59.00012: Density Functional Theory Studies of Protective Interlayer of Graphene for the Back Contact of Copper Zinc Tin Sulphur Thin Film Solar Cell Yau Lun Felix Chong, Junyi Zhu CZTS(Se) based solar cell is one of the promising candidates in the development of the 3rd generation solar cell absorbers. However, the efficiency of CZTS is insufficient for commercial product. One of the major causes of low performance is poor back contact-absorber interface quality. During annealing process of CZTS, S atom diffuses into Mo back contact layer and form a detrimental secondary phase of MoS2. Interlayer engineering has been proposed. However, most of the proposed interlayers are based on insulating systems. Here, we propose a new protective material of graphene as an effective diffusion barrier to block any S atom diffusion. Using Climbing Image Nudged Elastic Band Method based on Density Functional Theory calculation to find diffusion barrier and minimum energy path, we can show that the choice of our protective layer can effectively block S atoms diffusion under fabrication and operation environment. We also calculated the band alignment between the proposed protective interlayer and CZTS absorption layer. The results suggest the protective interlayer we proposed will not significantly degrade the performance of the solar cell. |
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