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 J59: Electronic Structure: Thermodynamic and Optical PropertiesLive
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Sponsoring Units: FIAP Chair: Thuc Mai, National Institute of Standards and Technology |
Tuesday, March 16, 2021 3:00PM - 3:12PM Live |
J59.00001: Optical Properties of Cs2AgBiBr6 Collin Tower, Maureen Reedyk
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Tuesday, March 16, 2021 3:12PM - 3:24PM Live |
J59.00002: Quasiparticle energies and excitonic effects of chromium trichloride Linghan Zhu, Li Yang Recently fabricated two-dimensional (2D) van der Waals (vdW) magnetic structures provide precious opportunities to study many-electron interactions and excited state properties of correlated materials under quantum confinement. Employing first-principles many-body perturbation simulations, we reveal enhanced excitonic effects in 2D and bulk forms of magnetic CrCl3. Unlike usual nonmagnetic vdW semiconductors, in which excited state properties are sensitive to dimensionality, many-electron interactions dominate quasiparticle energies and optical responses of both two-dimensional and bulk CrCl3. The calculated electron-hole (e-h) binding energy can reach 3 eV in monolayer and remains as high as 2 eV in bulk. Particularly, the two-particle e-h binding energy is more sensitive to the quantum confinement than the single-particle self-energy correction. As a result, an unusual red shift of the "optical gap" is observed in thinner samples, which is opposite to the widely observed blue shift trend in nanostructures. The unusual quantum confinement effect in CrCl3 extends our understanding of many-electron interactions in the vdW magnets. |
Tuesday, March 16, 2021 3:24PM - 3:36PM Live |
J59.00003: Understanding Optomechanical properties of TaS2 from first principles Anubhab Haldar, Cristian Cortes, Stephen Gray, Sahar Sharifzadeh, Pierre Darancet The 1T phase of tantalum disulfide, 1T-TaS2, is a layered van der Waal's material exhibiting commensurate charge density waves (CCDWs) that significantly alter its dielectric properties and are associated with a metal-insulator transition. Here, we utilize first-principles density functional theory (DFT) and time-dependent TDDFT to investigate the optomechanical response of 1T-TaS2. Simulations of the optical dielectric function show a transition from an anisotropic dielectric to a hyperbolic medium response in the visible frequency to mid-IR frequency regime. Additionally, we combine TDDFT simulations with a phenomenological model to describe the electron-phonon-mediated phase transition upon exposure to near- and mid-infrared pulsed illumination. We predict that the response of the material is highly sensitive to the wavelength and direction of the incoming far-field radiation. |
Tuesday, March 16, 2021 3:36PM - 3:48PM Live |
J59.00004: Analysis of critical points in temperature dependent and time resolved ellipsometry spectra of Ge using digital filtering Carola Emminger, Farzin Abadizaman, Nuwanjula Samarasingha Arachchige, Jose Menendez, Shirly Espinoza, Steffen Richter, Mateusz Rebarz, Oliver Herrfurth, Martin Zahradník, Rüdiger Schmidt-Grund, Jakob Andreasson, Stefan Zollner We analyze critical points (CPs) in the dielectric function (DF) of Ge measured with static and time-resolved spectroscopic ellipsometry. Data were taken between 10 K and 718 K to investigate the temperature dependence of the direct band gap E0. To obtain lineshape parameters, the second energy derivatives of the DF are calculated using a linear filter technique based on Gaussian kernels introduced by Le et. al.1 which combines interpolation, noise reduction, and scale change. Taking into account excitonic effects, a Tanguy lineshape is fitted to the second derivatives of the DF. A red shift of energy and an increase in broadening with rising temperature are found and are fitted using a Bose-Einstein factor considering electron-phonon interaction. |
Tuesday, March 16, 2021 3:48PM - 4:00PM Live |
J59.00005: Tuning the Magnetostructural Phases of Pr2O3 with Pressure and Magnetic Field John Slimak, Astha Sethi, Taras Kolodiazhnyi, Lance Cooper The energetic proximity of crystal electric field (CEF) and phonon excitations in rare-earth materials can produce many realizations of strong electron-phonon coupling. We present temperature-, pressure-, and magnetic field-dependent Raman scattering measurements of Pr2O3, which reveal phonon anomalies, CEF excitations, and evidence for strong phonon-CEF coupling. We show that both an applied magnetic field and pressure induce a similar splitting of the doubly degenerate first excited CEF level, suggesting that pressure and magnetic field have the similar effect of splitting the doubly degenerate CEF excited state into singlet states having opposite angular momenta. We suggest that Pr2O3 shows promise for observing pressure-induced magnetic order at sufficiently high pressures. |
Tuesday, March 16, 2021 4:00PM - 4:12PM Live |
J59.00006: What is origin of visible photoluminescence in the lead-free double-perovskite Cs2InAgCl6? Viet-Anh Ha, Hyungjun Lee, George Volonakis, Feliciano Giustino The halide double perovskite Cs2InAgCl6 was recently designed in silico and synthesized as a novel lead-free direct band gap semiconductor [G. Volonakis, et al., J. Phys. Chem. Lett. 8, 772 (2017)]. This perovskite exhibits a wide direct band gap above 3 eV, and also shows exceptional photoluminescence (PL) in visible range when doped with Na or Bi [J. Luo, et al., Nature 563, 541 (2018); F. Locardi, et al., ACS Energy Lett. 4, 8, 1976 (2019)]. This phenomenon has been exploited to successfully design stable white-light-emitting diode with PL quantum yield of more than 86 % [J. Luo, et al., Nature 563, 541 (2018); S. Li et al., ACS Appl. Mater. Interfaces 12, 46330 (2020)]. In this work we address the question of what is the underlying physical mechanism of the PL in Cs2InAgCl6. To this aim we perform calculations of band structures and optical spectra using hybrid functionals and the GW method, and we investigate the electronic properties of characteristics defects in relation to the observed PL signal. |
Tuesday, March 16, 2021 4:12PM - 4:24PM Live |
J59.00007: Effect of Pulsed Laser Annealing on the optoelectronic properties of ZnO thin films Md Abu Zobair, Bishwajite Karmakar, M.F.N. Taufique, Ariful Haque, Kartik Ghosh ZnO thin films have attracted great attention recently due to their unique electronic and optical properties. Though these wide bandgap semiconductors are inherently n-type due to oxygen vacancies, both n-type and p-type ZnO is required for their effective implementation in electronic devices. This research aims to achieve p-type semiconductor through pulsed laser annealing (PLA) and controlling other electronic and optical properties necessary for optoelectronic applications. Thin films of ZnO have been grown on different substrates using pulsed laser deposition and spin coating. Then PLA of the film is done by changing laser parameters (Energy, Frequency, pulse width, number of shots) in different environments. Structural quality of the annealed films is investigated using X-ray diffraction, Electron microscopy, Raman spectroscopy, and X-ray photoelectron spectroscopy. Optoelectronic properties of the PLA films are investigated using UV-VIS and photoluminescence spectroscopy and Electrical transport measurement. Structural properties are also investigated from MD simulation and DFT calculation for both bulk and thin film of ZnO to validate the experimental data. The detailed analysis of experimental data and simulation results will be discussed in this presentation. |
Tuesday, March 16, 2021 4:24PM - 4:36PM Live |
J59.00008: Influence of Quantum Dot Morphology on the Optical Properties of GaSb/GaAs Multilayers Christian Greenhill, Alexander Chang, Eric Zech, Stephen Clark, Ganesh Balakrishnan, Rachel Goldman We examine the influence of quantum dot (QD) morphology on the optical properties of two-dimensional (2D) GaSb/GaAs multilayers, with and without three-dimensional nanostructures. Using nanostructure sizes from scanning transmission electron microscopy and local Sb compositions from local-electrode atom-probe tomography as input into self-consistent Schrodinger–Poisson simulations based on 8 x 8 kp theory, we compute confinement energies for GaSb QDs, circular arrangements of smaller QDs, termed QD-rings, and 2D layers on GaAs substrates. The computed confinement energies and the measured photoluminescence emission energies increase from QDs to QD-rings to 2Dlayers, enabling direct association of nanostructure morphologies with the optical properties of the GaSb/GaAs multilayers. This work opens opportunities for tailoring near to far infrared optoelectronic devices by varying the QD morphology. |
Tuesday, March 16, 2021 4:36PM - 4:48PM Live |
J59.00009: Modeling optical absorption in GeSn alloys for photonic device applications Michael Johnson (Pending APS Join), Zairui Li, Jay Mathews Germanium tin alloys are an attractive material system because of their compatibility with silicon and their optical properties in the infrared range. These properties give GeSn alloys potential to be used for low-cost, high-efficiency photonic devices like photodetectors, LEDS, and infrared lasers that can be integrated with silicon electronics. The optical properties of GeSn, namely the absorption coefficient and spontaneous emission levels, are dependent on the material’s composition, strain, and the density of unoccupied states in the conduction band. Pure germanium is an indirect band gap material but can transition to a direct gap material with high levels of strain. Sn, a direct gap material, is introduced into the lattice allowing a transition to a direct gap material. A direct gap material is favorable because emission is possible without phonon assistance, which is required in indirect gap materials, thereby increasing optical absorption and emission. We use modeling to predict the absorption coefficient of GeSn alloys near the direct band gap with various amounts of Sn and strain. The model includes the effects of strain on the band structure as well as the occupation of the conduction band states, which can dramatically affect the absorption and emission properties. |
Tuesday, March 16, 2021 4:48PM - 5:00PM Live |
J59.00010: A novel fundamental bound on effective masses in photovoltaic materials Ella Banyas, Liang Tan The development of generalized methods for predicting electronic properties from atomic structure presents a key challenge in materials design. Photovoltaics, for example, require a high carrier mobility in addition to an ideal band gap; but identifying such materials from their large design space can be difficult because of computational cost and database quality limitations. As an effort to theoretically investigate the links between atomic and electronic structure, we use a local orbital-based approach and the nearsightedness principle of Prodan and Kohn to derive a novel analytic bound on the effective mass, which is inversely proportional to carrier mobility in the Boltzmann transport limit. We compare this bound to both experimental and simulated data from a high-throughput search of the Materials Project, and by projecting the first-principles data onto local Wannier functions, we assess the efficacy of the bound’s descriptor variables. |
Tuesday, March 16, 2021 5:00PM - 5:12PM Live |
J59.00011: Combined impact of resonance bond engineering and Peierls distortion on electronic density of states in bulk Ge2Sb2Te(5-5x)Se5x p phase change materials Utpal Chatterjee, Junjing Zhao, Zhenyang Xu, Junqiang Li, Despina A Louca, Gia-wei Chern We report studies on bulk Ge2Sb2Te(5-5x)Se5x (GSST) phase change material (PCM) single crystals, where x represents the amount of Selenium (Se) substituting Tellurium (Te) in Ge2Sb2Te5. Using results from photoemission spectroscopy, x-ray diffraction and Raman scattering experiments together with numerical simulations. we explore tunability of resonance bonding (RB) and its impact on the electronic structure of GSST in the crystalline phase. We present direct evidence for (i) finite electronic density of states (DOS) at the chemical potential for all measured x as expected in the crystalline phase, and (ii) an unusual suppression in the DOS with increasing x over an energy range comparable to the entire valence band. Using numerical works, we show that these observations can naturally be interpreted by a gradual weakening of resonance bonding accompanied by an enhancement in Peierls-type distortion with increasing substitution of Te by Se, which is counterintuitive since the modification in RB of a PCM is commonly perceived to occur during crystal to amorphous transition. |
Tuesday, March 16, 2021 5:12PM - 5:24PM Live |
J59.00012: A model of dephasing in shift current processes Benjamin Fregoso The shift current, a nonlinear effect, is thought to be an important transport mechanism in many ferroelectrics and to carry information about the geometry of the Bloch wave function. Contrary to standard transport processes, it depends on the off-diagonal elements of the density matrix and not on the occupation of energy levels. We construct a simple model of dissipation beyond the relaxation-time approximation for shift current processes for electrons in a one-dimensional chain of ions lacking inversion symmetry and coupled to external electric and magnetic fields. The model allows to study if and how the system reaches non-equilibrium steady states. |
Tuesday, March 16, 2021 5:24PM - 5:36PM Live |
J59.00013: Temperature dependence of optical phonon bands in GaP Nuwanjula Samarasingha Arachchige, Stefan Zollner We explore the effect of temperature on the frequency and linewidth of transverse (TO) and longitudinal (LO) optical phonons in bulk gallium phosphide (GaP) using FTIR ellipsometry from 0.03 to 0.80 eV from 80-720 K. We extract the optical phonon features of GaP by fitting our ellipsometric spectra with the Lowndes–Gervais model, which applies two different broadening parameters to the TO and LO phonons. In GaP, the two-phonon density of state is larger for the decay of TO phonons than for LO phonons. Therefore, we observed a large TO phonon broadening and an asymmetric reststrahlen line shape (compared to the LO phonon). This leads to a negative dielectric constant (ε2) just above the LO phonon. Two-phonon absorption can be added in the model to avoid this negative ε2. We find a temperature dependent redshift and broadening of TO and LO phonons with increasing temperature due to anharmonic phonon-phonon decay [1]. These temperature dependent phonon features can be described by three and four phonon decay processes. Also, we investigate the temperature-dependence of the high-frequency dielectric constant. Its variation is explained by thermal expansion and the temperature dependence of the band gap. |
Tuesday, March 16, 2021 5:36PM - 5:48PM On Demand |
J59.00014: Origins of giant optical anisotropy in quasi-one-dimensional transition metal chalcogenides Guodong Ren, Boyang Zhao, Arashdeep Thind, Jad Salman, Nan Wang, Tengfei Cao, John Cavin, Han Wang, Mikhail Kats, Jayakanth Ravichandran, Rohan Mishra Hexagonal perovskite sulfides, such as BaTiS3, with one-dimensional chains of face-sharing TiS6 octahedral units show giant optical anisotropy [1]. Here, we present results of a joint theoretical and experimental investigation of the role of structure and composition on the electronic and optical properties of BaTiS3 and Sr1+xTiS3. Using first-principles calculations, we predict several phase transitions driven by soft phonon modes in BaTiS3, and study the optical anisotropy among these phases. In Sr1+xTiS3, we reveal the effect of non-stoichiometry on the crystal structure, electronic and optical properties. Our experimental studies on structural and optical properties of these materials support our theoretical results. This work will provide guidelines for designing materials with giant optical anisotropy. |
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