Bulletin of the American Physical Society
APS March Meeting 2019
Volume 64, Number 2
Monday–Friday, March 4–8, 2019; Boston, Massachusetts
Session L22: Electrons, Phonons, Electron-Phonon Scattering and Phononics IIIFocus
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Sponsoring Units: DCOMP DMP Chair: Lucas Lindsey Room: BCEC 157C |
Wednesday, March 6, 2019 11:15AM - 11:51AM |
L22.00001: Electron-phonon coupling and electronic transport in n-type PbTe: Insights from first principles calculations Invited Speaker: Ivana Savic Exploiting the fascinating properties of materials near soft mode phase transitions is an emerging concept in the quest to increase thermoelectric efficiency [1]. Soft phonons may lead to low lattice thermal conductivity, while preserving high electronic conductivity. Here I will focus on the unusual electronic transport properties of n-type PbTe, which is a classic thermoelectric material that exists near a soft optical mode phase transition. Our first principles calculations show that longitudinal optical phonon scattering dominates electronic transport, while acoustic phonon scattering is relatively weak [2,3]. We find that scattering due to soft transverse optical phonons is by far the weakest scattering mechanism, due to the symmetry-forbidden scattering between the conduction band minima and the zone center soft modes [3]. Soft phonons thus play the key role in the high thermoelectric figure of merit of n-type PbTe: they do not degrade its electronic transport properties although they strongly suppress the lattice thermal conductivity [1]. |
Wednesday, March 6, 2019 11:51AM - 12:03PM |
L22.00002: Predictive calculations of phonon-limited carrier mobilities in semiconductors Samuel Ponce, Elena Roxana Margine, Martin Schlipf, Feliciano Giustino In this talk, we will probe the accuracy limit of ab initio calculations of carrier mobilities that relies on the electron-phonon coupling, within the framework of the Boltzmann transport equation. In particular, we will show that predictive calculations of electron and hole mobilities require many-body quasiparticle corrections to band structures and electron-phonon matrix elements, the inclusion of spin-orbit coupling, and an extremely fine sampling of inelastic scattering processes in momentum space [1]. |
Wednesday, March 6, 2019 12:03PM - 12:15PM |
L22.00003: Stochastic properties of a hot electron gas in a semiconductor from first-principles Alexander Choi, Austin Minnich Recent advances in ab-initio methods have enabled the routine calculation of the electronic transport properties of crystals. Analogous calculations of stochastic properties, such as the spectral noise power of an electron gas driven by an electric field, have not yet been reported despite their importance in setting fundamental detection limits of microwave electronics. Here, we report an ab-initio treatment of the noise of a driven electron gas using a Boltzmann-Green’s function approach. Our approach combines electronic structure and scattering rates from first-principles with a numerically exact solution of the Boltzmann equation, providing a parameter-free description of stochastic transport processes in a semiconductor. The insights derived our ab-initio approach will facilitate the realization of semiconductor devices operating near the quantum noise limit. |
Wednesday, March 6, 2019 12:15PM - 12:27PM |
L22.00004: Probing electron-phonon interactions in Weyl semimetal using Raman spectroscopy and anharmonic phonon calculations Kunyan Zhang, Fei Han, Shun-Li Shang, Zi-Kui Liu, Mingda Li, Shengxi Huang TaP, a type of Weyl semimetal (WSM) with noncentrosymmetric space group I41md, is a special type of quantum materials that have attracted strong recent interests. The gapless band structure of TaP allows unique optical response and transport phenomena. Although electrical and photoemission characterizations such as Hall measurement and angle-resolved photoemission spectroscopy (ARPES) have been performed on various WSMs, there is insufficient research on the electronic and optical properties using optical spectroscopies as probes. In the present work, the light-matter interactions, including electron-phonon and electron-photon interactions, have been studied comprehensively through phonon-based Raman spectroscopy and first-principles calculations. We demonstrate how the optical spectroscopic responses, such as Raman and absorption, of TaP change under various physical parameters including crystal orientation, temperature, and excitation laser energies. Advanced first-principles calculations of electronic and especially anharmonic phonon properties have been employed to unveil the measured optical spectroscopic responses and their relationship with electronic performance of WSMs. |
Wednesday, March 6, 2019 12:27PM - 12:39PM |
L22.00005: High Temperature Charge Transport In Strontium Titanate Clement Collignon, Benoit Fauque, Kamran Behnia Strontium titanate quickly becomes metallic upon doping, but while the fermiology of this metallic phase is well understood its transport properties remain elusive [1]. |
Wednesday, March 6, 2019 12:39PM - 12:51PM |
L22.00006: Band structure and optical properties of boron arsenide (BAs): effects of quasiparticle corrections, spin-orbit coupling, and phonon-assisted optical transitions Kyle Bushick, Kelsey Mengle, Nocona Sanders, Emmanouil Kioupakis The III-V semiconductor BAs is best known for its high thermal conductivity, which was computationally predicted and recently experimentally validated. However, due to a lack of high-quality samples, the electronic and optical properties have not been systematically explored. We use density functional and many body perturbation theory including quasiparticle and spin-orbit coupling corrections to systematically characterize the electronic and optical properties of BAs. Accurate calculations of band gap values, carrier effective masses, and dielectric functions yield insights into the fundamental properties of this new material. We further explore the effect of phonon-mediated transitions across the indirect band gap on the optical properties. We will discuss the implications of our findings on potential applications of BAs to semiconductor technologies. |
Wednesday, March 6, 2019 12:51PM - 1:03PM |
L22.00007: Ab initio studies of electron-phonon coupling to the electron self-energy in organic crystals Florian Brown-Altvater, Gabriel Antonius, Tonatiuh Rangel Gordillo, Matteo Giantomassi, Claudia Draxl, Xavier Gonze, Steven G. Louie, Jeffrey B Neaton Organic crystals combine properties of individual molecules and extended periodic systems. They garner much scientific interest due to their high charge carrier mobilities, and because their unique electronic and vibrational properties challenge our understanding of fundamental optoelectronic processes. In this work we use density functional perturbation theory to study the phonon-scattering lifetimes, as well as the temperature dependence of the band structure. We find that a self-consistent approach to the electron self-energy due to electron-phonon coupling yields qualitative differences compared to a conventional approach, and shows much better agreement with experimental results. We discuss efficient methods for self-consistency in organic crystals, and implications on calculating band gap renormalization and quasiparticle lifetimes of these systems. |
Wednesday, March 6, 2019 1:03PM - 1:15PM |
L22.00008: Ab initio exciton and phonon dynamics in Transition Metal Dichalcogenides Pedro Melo, Matthieu Verstraete, Zeila Zanolli The interest in the properties of transition metal dichalcogenides (TMDs) has increased due to the discovery of the coupling between spin and valley degrees of freedom, which can be seen experimentally using a circularly polarised laser. After excitation the newly formed carrier populations must move towards the other valley until balance is reached. However, this relaxation process is not entirely understood in the literature, where the relative importance of the electron-electron (e-e) or electron-phonon (e-p) interactions is still a subject of debate. Previous works on WSe2 [A. Molina-Sánchez, et al - Nano letters, 2017] have shown that the e-p interaction is a good candidate to describe the relaxation process. Using a fully ab-initio framework based on the Baym-Kadanoff equations [P. M. M. C. de Melo and A. Marini, Phys. Rev. B 93, 155102 (2016)] we study the influence of the e-p interaction on MoSe2 after its excitation by a laser field. We show how phonons allow carrier relaxation and how the Kerr signal and total magnetisation are affected at different temperatures, with the latter exhibiting a non-monotonic behaviour as the temperature increases. |
Wednesday, March 6, 2019 1:15PM - 1:27PM |
L22.00009: Ab Initio Electronic T1 Spin Relaxation Times in Silicon and Diamond Jinsoo Park, Jin-Jian Zhou, Marco Bernardi Spin relaxation in inversion-symmetric crystals primarily occurs through the Elliott-Yafet mechanism, in which the injected spins are scattered by impurities at low temperatures and phonons at higher temperatures. We present an efficient first-principles approach for computing the phonon-limited Elliott-Yafet electronic spin relaxation time T1 in materials ranging from metals to semiconductors and insulators. Our scheme combines fully-relativistic ab initio electron-phonon scattering with a novel approach to correctly treat Kramers degenerate electronic states. Application of our approach to silicon and diamond is discussed in this talk, where we analyze the temperature dependence of the spin relaxation times together with the contributions from intravalley and intervalley processes. The computed spin relaxation times in silicon are in excellent agreement with experiment above 50 K. Our work enables accurate ab initio calculations of the T1 spin relaxation time in a range of materials, including topological ones, providing new microscopic insight into spin relaxation. |
Wednesday, March 6, 2019 1:27PM - 1:39PM |
L22.00010: Quantum-kinetic theory for electron-diffusion and phonon-drag thermoelectric powers from drifting electrons in a quantum wire Richard Zhang, Danhong Huang Thermal conditions during an ultrafast femtosecond-scale laser pulse are difficult to resolve due to phonon vibration drag behind an electron excitation. The motivation behind this study is to establish a ground-up quantum dynamics model to predict elastic wave effects in a confined electron-phonon state. We established transient collision equations from three-phonon coupled anharmonic interactions to obtain the evolution of hot phonon species distribution and thermoelectric response in a confined-size semiconductor material, such as a GaAs nanowire subjected to a spatially uniform DC electric field. A simplified diatomic chain model was chosen to represent longitudinal phonon dispersion. A quasi-steady state was observed in electron-phonon drift-drag response and settling of low frequency phonon-phonon scattering. We also studied the effects from phonon-surface boundary parameters, such as fluctuation strength and interaction length. As new materials with surprising measured transport properties are being found, further development of this unifying theory of carrier-lattice dynamics has potential for capturing ephemeral excitations in various solids. |
Wednesday, March 6, 2019 1:39PM - 1:51PM |
L22.00011: Electron-phonon coupling from ab initio linear-response theory within the GW method: Method and applications to oxide superconductors Zhenglu Li, Gabriel Antonius, Meng Wu, Felipe Da Jornada, Steven G. Louie We present a first-principles linear-response theory of changes due to perturbations in the quasiparticle self-energy operator within the GW method. This approach, named GW perturbation theory (GWPT), is applied to calculate the electron-phonon (e-ph) interactions with the full inclusion of the GW non-local, energy-dependent self-energy effects, going beyond density-functional perturbation theory. Unlike the frozen-phonon approach, GWPT gives access to e-ph matrix elements at the GW level of all phonons, and the computational cost scales linearly with the number of phonon modes (wavevectors and branches) investigated. We present results of correlation-enhanced superconductivity in Ba0.6K0.4BiO3 and of e-ph physics in other oxide superconductors where many-electron effects are strong. |
Wednesday, March 6, 2019 1:51PM - 2:03PM |
L22.00012: First-principles study of electron-phonon interactions in SrTiO3 Nikolaus Kandolf, Carla Verdi, Feliciano Giustino
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Wednesday, March 6, 2019 2:03PM - 2:15PM |
L22.00013: Exciton-phonon interactions in organic crystals from first principles many-body perturbation theory Jonah Haber, Sivan Refaely-Abramson, Gabriel Antonius, Felipe Da Jornada, Steven G. Louie, Jeffrey B Neaton Molecular crystals are attractive candidates for solar energy conversion applications due to their strong light-matter interactions, nearly endless structural tunability, and the relative inexpense with which they can be synthesized and processed. Acene crystals, such as tetracene and pentacene, possess both strong electron-hole and significant electron-phonon interactions, and a thorough understanding of the photophysics of these materials requires a careful analysis of the interplay between the ionic and excitonic degrees of freedom. In this talk, we present our linear response framework for computing exciton-phonon matrix elements, using ab initio density functional perturbation theory and many-body perturbation theory within the GW plus Bethe-Salpeter equation approach. We apply this method to compute exciton-phonon scattering rates for spin-singlet and spin-triplet excitons in prototypical acene crystals and compare with experimental linewidths. Finally, we discuss the implications of our calculations for exciton diffusion and multiexciton generation in these extended organic systems. |
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