Bulletin of the American Physical Society
APS March Meeting 2019
Volume 64, Number 2
Monday–Friday, March 4–8, 2019; Boston, Massachusetts
Session R22: Electrons, Phonons, ElectronPhonon Scattering and Phononics VFocus

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Sponsoring Units: DCOMP Chair: Mu Wang, American Physical Society Room: BCEC 157C 
Thursday, March 7, 2019 8:00AM  8:12AM 
R22.00001: Thermal conductance for one dimensional disordered harmonic chains. Biswarup Ash, Ariel Amir, Yuval Oreg, Yoseph Imry We study heat conduction in one dimensional disordered harmonic chain of particles with longitudinal motion. We observe intriguing scaling behavior for the thermal conductance depending on the nature of the disorder and the coupling of the system with the heat bath. We show that the heat transport is 'anomalous' for an uniformly disordered chain, irrespective of the strength of the disorder and the coupling to the heat bath. Using a simple scaling relation, we show that thermal conductance scales with the system size (L) as L^{0.5} in this system. We further demonstrate that the scaling behavior for thermal conductance gets altered dramatically as we change the nature of the disorder. Particularly, we show that for disorder characterized by a 'heavytailed' probability distribution, the heat transport follows Fourier’s law when the coupling of the system with the thermal reservoir is weak. The different scaling behavior observed in the different models are shown to be intimately connected with the scaling properties of density of states and localization length of the phonons in the disordered systems. 
Thursday, March 7, 2019 8:12AM  8:24AM 
R22.00002: Spectral picture of thermal phonon Anderson localization in binary superlattices Taneli Juntunen, Ilkka Tittonen In the emerging field of phononics, wave effects such as Anderson localization are expected to provide essential insight for quenching of heat transport in, e.g., thermoelectric applications. However, the currently limited understanding of Anderson localization in phononic systems leaves its prospect for potential practical applicability in heat management an open question. Our atomistic study on disordered binary superlattices provides a systematic avenue for exploiting phononic wave localization, achieving an ultralow thermal conductivity and an anomalously large thermal anisotropy in realistic semiconductor systems at ambient conditions. We provide a detailed spectrally decomposed description on the interrelationship between wave interference, anharmonicity, and incoherent impurity scattering. Finally, fundamental insight on the origin of phononic localization is elucidated through harmonic analysis. 
Thursday, March 7, 2019 8:24AM  8:36AM 
R22.00003: Anharmonically Excited Phonons as an Approach to Controlled Optical Materials: a First Principles Study Guru Bahadur Khalsa, Jeffrey Moses, Nicole Benedek

Thursday, March 7, 2019 8:36AM  9:12AM 
R22.00004: From electronphonon transport properties to computational discovery of new materials for energy conversion. Invited Speaker: Boris Kozinsky We introduce a novel simplified approach for computing electronic transport properties of complex semiconductors and lowdimensional quantum materials, without empirically fitted parameters. Using this method allowed us to discover new thermoelectric alloy compositions with leading performance and stability. The computational approach achieves good accuracy and transferability while greatly reducing complexity and computation cost compared to the existing methods. The firstprinciples calculations of the electronphonon coupling demonstrate that the energy dependence of the electron relaxation time varies significantly with chemical composition and carrier concentration, suggesting that it is necessary to go beyond the commonly used approximations to screen and optimize materials' composition, carrier concentration, and microstructure. The new method is verified using high accuracy computations and validated with experimental data before applying it to screen and discover promising compositions in the space of halfHeusler alloys. We discuss the universality of the WiedemannFranz law and deviations from it in semiconductors, computing the Lorenz number from first principles. 
Thursday, March 7, 2019 9:12AM  9:24AM 
R22.00005: Influence of Oxygen Phonon Coupling on Fluctuating Stripes in the Threeband Hubbard Model Tianyi Liu, Edwin Huang, Brian Moritz, Thomas Devereaux The normal state of highT_{c} cuprate superconductors is characterized by competition between multiple ordered states such as antiferromagnetism, chargedensitywaves, and stripes. We use determinant quantum Monte Carlo (DQMC) simulations of the threeband Hubbard model with oxygen phonon coupling to investigate how electronphonon coupling influences hightemperature fluctuating stripes, in relation to doping level, phonon properties and electronphonon coupling strength. Quantities such as the spinspin and densitydensity correlation functions are extracted from the simulations to illustrate the influence of electronphonon coupling on stripes. 
Thursday, March 7, 2019 9:24AM  9:36AM 
R22.00006: Pressure enhanced superconductivity in MoTe_{2} Hari Paudyal, Samuel Ponce, Elena R Margine Molybdenum ditelluride (MoTe_{2}) has attracted significant research interest due to the discovery of exotic topological states and pressuredriven superconductivity. Firstprinciples calculations combined with the anisotropic MigdalEliashberg formalism have been carried out to investigate the role of electronphonon interaction and the superconducting pairing mechanism in the two structurally similar phases, T_{d} and 1T’, under pressure. We find that both phases are superconducting, with the centrosymmetric 1T’ phase displaying a slightly larger electronphonon coupling strength compared to the noncentrosymmetric T_{d} phase due to the softening of the lowenergy phonon modes and a small increase in the density of states at the Fermi level. 
Thursday, March 7, 2019 9:36AM  9:48AM 
R22.00007: A comparison of molecular dynamics and Boltzmann transport equation approaches for lattice thermal conductivity Marcello Puligheddu, Yi Xia, Maria Chan, Giulia Galli The predictive modeling of lattice thermal conductivity κ_{L} is of importance for both fundamental understanding and materials design. Molecular dynamics (MD) and Boltzmann Transport Equation (BTE) are the two most common approaches used to predict κ_{L}. In this work, we perform a comprehensive comparison between MD and BTE approaches, on two model systems (MgO and PbTe), using interatomic potentials. Comparisons between MD and lifetimes from three and fourphonon scattering, and between different treatment of statistics, are made. The sources of agreement and differences between MD and BTE are discussed. 
Thursday, March 7, 2019 9:48AM  10:00AM 
R22.00008: Fourphonon scatteringdominated linewidth of optical phonons Xiaolong Yang, Tianli Feng, Xiulin Ruan Optical phonon linewidth is crucial to infrared optical properties of polar materials and thermal conductivity of certain materials that have a large number of optical phonon branches. The current understanding is, however, still limited to the lowest order phonon scattering, and the predicted linewidths often have large discrepancy with experiment. In this work we show the significance of fourphonon scattering in determining infrared optical properties for a range of important materials, including cubic boron arsenide (BAs), cubic silicon carbide (3CSiC), and αquartz. Strikingly, We find that fourphonon scattering generally dominates optical phonon linewidths at elevated temperatures over threephonon scattering. In large band gapmaterials, e.g., BAs and AlSb, fourphonon scattering rates are found to be orders of magnitude higher than threephonon scattering rates even at room temperature. The predicted infrared optical properties of αquartz 
Thursday, March 7, 2019 10:00AM  10:12AM 
R22.00009: Firstprinciples study of structural phase transition and thermal transport in halide perovskite CsPbBr_{3} Terumasa Tadano, Wissam Saidi Halide perovskites have attracted significant attention in recent years for their excellent optoelectronic properties. While the optoelectronic properties of halide perovskites have been widely studied both experimentally and theoretically, their thermal properties have been studied only partially. In particular, firstprinciples study of phonon transport in halide perovskites is challenging because of the presence of unstable soft modes within the harmonic approximation. 
Thursday, March 7, 2019 10:12AM  10:24AM 
R22.00010: Firstprinciples calculation of ballistic photocurrents Liang Tan, Ruixiang Fei, Andrew Rappe The bulk photovoltaic effect (BPVE) is the generation of photocurrents in crystals with broken inversion symmetry. Ballistic currents, which arise from asymmetric phonon scattering, and shift currents, which are displacements of electrons upon photoexcition, have been proposed as mechanisms responsible for the BPVE under linearly polarized light. However, only the shift current contribution has been routinely studied with firstprinciples calculations. In this work, we present firstprinciples calculations of the phononinduced ballistic current contribution. These ballistic currents arise from an unbalanced momentum space distribution of carriers, which results from the interference of multiple carrierphonon scattering processes. We calculate the amplitudes of these processes using electronphonon interactions derived from density functional pertubation theory, to find the carrier distribution functions and the magnitudes of ballistic photocurrents. We apply this methodology to BaTiO_{3}, a typical ferroelectric which displays the BPVE. These results clarify the origin of the BPVE, and the relative importance of shift and ballistic currents. 
Thursday, March 7, 2019 10:24AM  10:36AM 
R22.00011: Lattice thermal conductivity calculations of αquartz and αcristobalite Atsushi Togo, Keiyu Mizokami, Isao Tanaka Lattice thermal conductivities of two SiO_{2} polymorphs, αquartz and αcristobalite, were studied using firstprinciples anharmonic phonon calculation and linearized phonon Boltzmann transport equation^{1}. Although αquartz and αcristobalite have similar phonon densities of states, phonon frequency dependencies of phonon group velocities and lifetimes are dissimilar, which results in largely different anisotropies of the lattice thermal conductivities. For αquartz and αcristobalite, distributions of the phonon lifetimes effective to determine the lattice thermal conductivities are well described by energy and momentum conservations of three phonon scatterings weighted by phonon occupation numbers and one parameter that represents the phononphonon interaction strengths. 
Thursday, March 7, 2019 10:36AM  10:48AM 
R22.00012: Phonon Anharmonicity: What Can Grüneisen Parameters Tell Us? Ethan Ritz, Nicole Benedek Phonon anharmonicity is essential for explaining phenomena such as thermal conductivity, thermal expansion, and the change in phonon frequencies with strain. In particular, strain dependence of phonon frequencies can be expressed through Grüneisen parameters, which are often used as a heuristic to quantify anharmonicity in general for a given system. However, the exact nature by which a system departs from anharmonicity is important  third, fourth, and higher order terms in the atomic potential play different roles in different situations. Are the same higher order force constants that contribute to Grüneisen parameters the ones involved in, for example, thermal transport processes, or the ones that cause the quasiharmonic approximation to fail at high temperature? Using both analytic methods and density functional theory to inform and understand the underlying features of anharmonicity for a variety of systems, we find that while Grüneisen parameters provide valuable insight for how phonon modes couple to strain, one must take care in relating this quantity to other anharmonic effects. We further explore the relationship between phonons and strain, and other couplings between periodic eigenfunctions and aperiodic perturbations. 

R22.00013: ABSTRACT WITHDRAWN

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