Bulletin of the American Physical Society
APS March Meeting 2019
Volume 64, Number 2
Monday–Friday, March 4–8, 2019; Boston, Massachusetts
Session V22: Electrons, Phonons, Electron-Phonon Scattering and Phononics VII |
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Sponsoring Units: DCOMP DMP Chair: Athanasios Chantis, Physical Review Materials, American Physical Society Room: BCEC 157C |
Thursday, March 7, 2019 2:30PM - 2:42PM |
V22.00001: Materials selection rules for optimum power factor in 2-dimensional
thermoelectrics Adithya Kommini, Zlatan Aksamija Thermoelectrics (TE) can improve the efficiency of power sources to meet ever-growing energy demand by converting waste heat into electricity. With the advent of new 2D materials and the knowledge of their material properties, the ability of these materials for future TE use need to be studied. Studies have predicted the stability of around 2000 van der Waals materials that can be exfoliated into 2D atomic films. Here, the distinct features of 2D materials like effective mass, density of states, and electron-phonon scattering deformation potentials are used to formulate simple material selection rules that can optimize TE power factor. These parameters are widely available in material databases or computationally inexpensive to calculate. Our simulations show that when inelastic scattering with optical phonons is dominant in a material, the TE power factor is highest with phonon energy of 5 kT. Further enhancement is possible with larger height in the step-like 2D density of states, lower effective mass, and higher degeneracy for the conduction band valley that participate in the transport. Employing these material selection rules help in identifying future thermoelectric materials that can have applications in thermal harvesting, thermal sensors, and electronic cooling. |
Thursday, March 7, 2019 2:42PM - 2:54PM |
V22.00002: Theory of generation and conversion of phonon angular momentum Masato Hamada, Shuichi Murakami Mechanical rotations in solids can be converted to magnetization and spin current via the spin-rotation coupling. Recently, in general solids, the phonon angular momentum has been formulated as the microscopic local rotation in the lattice. However, it usually cancels between phonon modes. In this talk, we propose the two ways of generation of phonon angular momentum in non-magnetic and magnetic insulators. In nonmagnetic insulators without inversion symmetry, a heat current induces the phonon angular momentum, in analogy with the Edelstein effect [1]. In magnetic insulators preserving the product of the inversion and time-reversal symmetries, the electric field can induce the phonon angular momentum, in analogy with the magnetoelectric effect. We also discuss microscopic mechanisms how the microscopic local rotations of atoms, i.e. the phonon angular momentum, is converted into electronic spins. |
Thursday, March 7, 2019 2:54PM - 3:06PM |
V22.00003: Impact of Quartic Anharmonicity on Lattice Thermal Transport in SnSe Yi Xia, Christopher Wolverton Layered SnSe has demonstrated exceptional thermoelectric properties with record high energy conversion efficiency, majorly owning to the ultralow lattice thermal conductivity. However, a fundamental understanding of the lattice dynamics and thermal transport properties is still lacking, particularly for the high temperature phase. The theoretical challenge originates from the second-order phase transition from low-temperature Pnma to high-temperature Cmcm phases between 700-800~K, wherein the Cmcm-SnSe displays lattice instability and imaginary phonon frequencies. To overcome this limitation, we go beyond harmonic approximation by further incorporating anharmonic phonon renormalization due to quartic anharmonicity. Moreover, both three- and four-phonon scatterings are accounted for in solving Phonon Boltzmann transport equation. We apply this strategy to perform a comparative study of lattice dynamics and thermal transport properties of SnSe at 300~K (Pnma) and 800~K (Cmcm). We reveal in detail the impacts of quartic anharmonicity on lattice stability, phonon quasiparticle energies and lattice thermal conductivities of both Pnma- and Cmcm-SnSe. Our theoretical calcualtions are in good agreement with experimental measurements performed on SnSe single crystals. |
Thursday, March 7, 2019 3:06PM - 3:18PM |
V22.00004: Optoacoustic spectrum of GaP: experiment and theory Andrey Baydin, Rustam Gatamov, Halina Krzyzanowska, Christopher J Stanton, Norman H Tolk GaP is an important indirect band gap material with variety of applications in optics ranging from LEDs to possible applications in GaP/Si based solar cells. We investigated the spectral dependence of the opto-acoustic response of GaP using time-domain Brillouin scattering. We found that the amplitude of the Brillouin oscillations varies significantly near the direct transition at Γ point. The developed theoretical model quantitatively explains the experimental data and shows that one can use coherent phonon spectroscopy to provide detailed information about electronic structure and optical transitions in indirect band gap materials. The results for GaP are also compared to GaAs and Si. |
Thursday, March 7, 2019 3:18PM - 3:30PM |
V22.00005: Electronic properties of IV-VI semiconductors obtained with G_{0}W_{0} including off-diagonal corrections Pablo Aguado-Puente, Piotr Chudzinski, Tchavdar Todorov, Jorge Kohanoff, Stephen B Fahy, Myrta Grüning The computation of electronic properties of IV-VI semiconductors constitutes a challenge for traditional density functional theory (DFT) methods. The underestimation of the bang gap by DFT can lead, in these materials, to a spurious band gap inversion that hinders the characterization of their electronic properties, and therefore the modeling of their thermoelectric performance. In addition, the G_{0}W_{0} approach often used to correct the DFT band structure also fails because of its perturbative nature, making necessary to improve the starting wavefunctions (e.g. using hybrid DFT) or to use more sophisticated approaches such as quasiparticle self-consistent GW. Here instead we use traditional DFT+G_{0}W_{0} with corrections from the relevant off-diagonal elements of the self-energy in order to obtain the band structure of some of these materials, e.g. PbTe. This method, which does not require adjustable parameters, is utilized to extract from first principles band structure characteristics necessary for the calculation of transport coefficients. Band gaps, effective masses and deformation potentials are obtained in good agreement and at a fraction of the computational cost of more sophisticated methods. |
Thursday, March 7, 2019 3:30PM - 3:42PM |
V22.00006: Temperature dependent electronic transport in concentrated solid solutions of the 3d-transition metals Ni, Fe, Co and Cr from first principles. German Samolyuk, Sai Mu, Andrew May, Sebastian Wimmer, Sergiy Mankovsky, Hubert Ebert, Brian Craig Sales, George Malcolm Stocks An approach to the calculation of transport coefficients is applied to the calculation of transport properties of fcc alloys of Ni, Fe, Co, Cr. The coherent potential approximation used to treat chemical disorder, temperature induced magnetic moment fluctuations and lattice vibrations via the alloy analogy. For the nonmagnetic alloys, Ni20Cr, and NiCoCr the combined effects of chemical disorder and lattice vibrations result in a monotonic increase in the resistivity as a function of temperature from an already large residual resistivity. For magnetic NiCo, NiFe, NiFeCo, additional electron scattering from magnetic fluctuations results in a rapid increase of the resistivity with temperature.The electronic part of the thermal conductivity in Ni20Cr, and NiCoCr, monotonically increases with temperature. In the magnetic alloys, electron scattering from magnetic fluctuations leads to an initial rapid decrease in thermal conductivity until this is overcome by an increasing number of carriers. |
Thursday, March 7, 2019 3:42PM - 3:54PM |
V22.00007: Bonding Hierarchy Induced High Thermoelectric Performance in Layered Zintl Compound BaAu_{2}P_{4} Koushik Pal, Jiangang He, Christopher Wolverton The search for new thermoelectric materials has gained rapid progress in recent years as thermoelectric technology offers the potential for environmentally friendly and sustainable energy conversion methods from waste heat to electricity. Using first-principles calculations based on density functional theory we show that bonding hierarchy gives rise to high thermoelectric performance in BaAu_{2}P_{4}, a layered Zintl compound with a small band gap. BaAu_{2}P_{4} exhibits crystallographic heterogeneity in which rigid [Au_{2}P_{4}]^{2−} units are separated by layers of Ba^{2+} cations, which are bonded relatively weakly to the lattice through electrostatic interactions. While the covalently bonded chains of phosphorus atoms facilitate large electrical conductivity, the presence of multiple bands near the Fermi level gives rise to an enhanced Seebeck coefficient. On the other hand, the loosely bound Ba along with the heavy Au atoms strongly scatter the heat carrying acoustic phonons, inducing a very low lattice thermal conductivity along the stacking direction. As a consequence of this coexisting rigid and fluctuating sublattices, BaAu_{2}P_{4} exhibits a large power factor and low lattice thermal conductivity, which results in a high thermoelectric figure of merit (zT). |
Thursday, March 7, 2019 3:54PM - 4:06PM |
V22.00008: Emergent localized states in twofold PT-symmetric ladder lattice. Jung-Wan Ryu, Sang-Jun Choi, Sungjong Woo, Ara Go, Nojoon Myoung, Hee Chul Park We have investigated the localized states at the interface of intertwined PT-symmetric systems which are robust against external pumping and damping. The intertwinement induces an additional PT-symmetry and interface exceptional points (EP) emerge and play the role of new critical points of non-Hermitian phenomena with bulk exceptional point. There are two distinct regimes possessing solidly localized states even though balanced gain and loss is increased. We obtain analytic expressions for the localization length and exceptional points in terms of tight-binding formalism. This theory is demonstrated by numerical calculation of eigenenergies and wave functions on quasi 1D ladder lattice and 2D bi-layered square lattice. |
Thursday, March 7, 2019 4:06PM - 4:18PM |
V22.00009: Local thermal current from cold to hot in a classical harmonic system with multi-path geometry Palak Dugar, Chih-Chun Chien The second law of thermodynamics forbids an overall flow of heat from a cold object to a hot one. However, it does not rule out a local heat flow from cold to hot in a multi-path geometry. |
Thursday, March 7, 2019 4:18PM - 4:30PM |
V22.00010: Activated lone-pair electrons lead to low lattice thermal conductivity: a case study of boron arsenide Guangzhao Qin, Ming Hu Due to the ability of firsthand solid-state conversion to electrical power from thermal energy, thermoelectrics have attracted a lot of attention for the valuable applications in reusing waste resources and thus may make crucial contributions to the crisis of environment and severe energy problems. Reducing the thermal conductivity is an efficient way to boost the thermoelectric performance. In this talk, I would like to introduce an effective way to realize low thermal conductivity by introducing lone-pair electrons or making the lone-pair electrons stereochemically active through bond nanodesigning. With proper bond nanodesigning, the intrinsic thermal conductivity of BAs is largely lowered, which thus would benefit its applications in thermoelectrics with further nanostructuring. Fundamental insight is gained for the underlying mechanism of the reduction of thermal conductivity. Similar approach can also extended to other semiconductor systems, such as silicon and gallium nitride. The approach for realizing low thermal conductivity and the underlying mechanism uncovered in this talk would largely benefit the design of thermoelectric devices with improved performance, especially in future researches involving novel materials for energy applications. |
Thursday, March 7, 2019 4:30PM - 4:42PM |
V22.00011: Anderson localization of surface plasmon polaritons in engineered disorder Ruwen Peng, Wen-BO Shi, R. H. Fan, Xian-Rong Huang, Mu Wang In this work, we experimentally demonstrate Anderson localization of surface plasmon polaritons (SPPs) at visible regime in metallic nanogratings with short-range correlated disorder. By increasing the degree of disorder, the confinement of SPPs is significantly enhanced, and the effective SPP propagation length dramatically shrinks. Strong localization of SPPs eventually emerges at visible regime, which is verified by the exponentially decayed fields and the vanishing autocorrelation function of the SPPs. Physically, the short-range correlated disorder induces strong interference among multiple scattered SPPs and provides an adequate fluctuation to effective permittivity, which leads to the localization effect. Our study demonstrates a unique opportunity for disorder engineering to manipulate light on nanoscale and may achieve various applications in random nanolasing, solar energy, and strong light-matter interactions. Reference: W. Shi, L. Liu, Ruwen Peng, D. Xu, K. Zhang, H. Jing, R. H. Fan, Xian-Rong Huang, Q. Wang, and Mu Wang, Nano Letters 18, 1896-1902 (2018). |
Thursday, March 7, 2019 4:42PM - 4:54PM |
V22.00012: Bipolaron insulators and polaron liquids in high-temperature superconductors Ba_{1-x}K_{x}BiO_{3} Shaozhi Li, Steven Johnston The Su-Schrieffer-Heeger (SSH) type electron-phonon (e-ph) coupling, arising from the modulation of the atomic overlap integrals, has been proposed as a driving mechanism formation of an insulating state in the high-temperature superconducting bismuthates Ba_{1-x}K_{x}BiO_{3}. However, this e-ph interaction has not been well studied in dimensions greater than one due to a lack of suitable numerical techniques. In this talk, we present a determinant quantum Monte Carlo (DQMC) method for simulating the SSH-type e-ph interaction in a three-orbital model defined on a two-dimensional Lieb lattice. At half-filling, we observe a bipolaron insulating phase characterized by a long-range dimerized distortion, where the ligand oxygens collapse and expand about alternating Bi atoms creating a bond-disproportionated state. This state is robust against moderate hole doping but is eventually suppressed at large hole concentrations, leading to a metallic polaron-liquid-like state with fluctuating patches of local dimerized distortions. Our result suggests that the polarons are highly disordered in the metallic state and freeze into a periodic array across the metal-to-insulator transition. Moreover, our results have broad implications for many perovskite materials, where the bond phonons are essential. |
Thursday, March 7, 2019 4:54PM - 5:06PM |
V22.00013: Lattice dynamics and superionic transition in ceria from first principles Sergei Simak We show how lattice dynamics in high-temperature ceria, CeO_{2}, can be studied beyond the quasiharmonic approximation [1]. The results indicate that the previously proposed precursor for the transition to the superionic phase is an artifact of the failure of the quasiharmonic approximation. We further directly observe the superionic transition at high temperatures [2]^{ }in our ab initio molecular dynamics simulations and find that it is initiated by the formation of oxygen Frenkel pairs. The Frenkel pairs are shown to form in a collective process involving simultaneous motion of two oxygen ions. |
Thursday, March 7, 2019 5:06PM - 5:18PM |
V22.00014: Kinetic Theory of Rectified Motion in a Smarticle Gas Zachary Jackson, William C Savoie, Shengkai Li, Kurt A Wiesenfeld, Daniel Goldman Smarticles are battery powered, self-deforming, three link robots that undergo a repeated prescribed gait. When a small number are confined inside an untethered ring the system undergoes undirected (isotropic) diffusion. Upon deactivation of one of the smarticles, the system displays directed diffusion, with speed and direction which depend on the mass of the confining ring. We present a collisional model that accurately predicts the directed motion. |
Thursday, March 7, 2019 5:18PM - 5:30PM |
V22.00015: Phase Stability of Dynamically Disordered Solids from First Principles Johan Klarbring, Serguei I Simak The study of phase stability in solid materials containing dynamic disorder, eg. solids with rotating molecular units, or superionic conductors, is a challenging problem in theoretical materials science. This is mainly due to the failure of the standard picture of atoms vibrating around fixed equilibrium positions, which makes theoretical phonon schemes inapplicable. Superionic conductors are dynamically disordered solid materials with exceptionally high rates of ionic conductivity, which makes them very promising solid electrolytes for fuel cells and solid-state batteries. |
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