Bulletin of the American Physical Society
APS March Meeting 2017
Volume 62, Number 4
Monday–Friday, March 13–17, 2017; New Orleans, Louisiana
Session H8: Electrons, Phonons, and Electron Phonon Scattering IIFocus

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Sponsoring Units: DCOMP Chair: David Singh, University of Missouri Room: 267 
Tuesday, March 14, 2017 2:30PM  2:42PM 
H8.00001: Firstprinciples modeling of resonant Raman scattering for the understanding of phonons and electrons in nanomaterials Liangbo Liang, Vincent Meunier, JiaAn Yan, Bobby Sumpter Raman spectroscopy is a popular tool that can probe both phonons and electrons of the materials. Firstprinciples modeling is important in aiding the understanding of experimental data. Raman modeling is typically based on the classical Placzek approximation and limited to the nonresonant condition, and thus the laser energy dependence of Raman intensities could not be captured. Here we showed that resonant Raman scattering could be captured by upgrading the classical approach, i.e., by calculating the dynamic dielectric tensor at the laser energy instead of the commonly used static value at zero energy. Our method was successfully applied to recently synthesized atomically precise graphene nanoribbons, and revealed the photonenergydependent Raman intensity of the radial breathing like mode (RBLM), which explained experimental observations that RBLM can be only observed in certain laser energies. Additionally, we also explored anisotropic 2D material, ReS2, and found that the angleresolved Raman polarization dependence of its Raman modes is sensitive to the laser energy, as confirmed by recent experiments. The intricate electronphonon coupling could lead to no simple rule for using Raman polarization dependence to determine the crystalline orientation. [Preview Abstract] 
Tuesday, March 14, 2017 2:42PM  2:54PM 
H8.00002: Nonadiabatic electronphonon coupling and hot carrier relaxation in amorphous silicon TaeHo Park, Mark Lusk Energy and optoelectronics applications for quantum confined silicon dots generally require an efficient means of collecting and distributing charge carriers. This has led us to consider quantum dots encapsulated within a hydrogenated amorphous silicon matrix which plays a critical role in photon collection, hot carrier cooling and transport. A theoretical framework to quantify the phonon assisted charge transfer and the carrier relaxation rates in both amorphous and crystalline Si has been developed based on nonadiabatic coupling (NAC). The vibrational part in these rates is obtained analytically using an extended FrankCondon formulation, while the electronic part is numerically calculated using a combination with TimeDependent Density Functional Theory (TDDFT) and Density Functional Perturbation Theory (DFPT). We use this new methodology to predict cooling rates and transport mobilities for amorphous silicon, and these predictions compare well with experimental measurements. The approach is then extended to calculate analogous values for nanocrystalline silicon, allowing us to propose a likely conduction mechanism for carrier transport through such mixed amorphous/crystalline materials. [Preview Abstract] 
Tuesday, March 14, 2017 2:54PM  3:06PM 
H8.00003: Electronphonon interactions in transport properties of WO$_{3}$ Wennie Wang, Youngho Kang, Burak Himmetoglu, Karthik Krishnaswamy, Anderson Janotti, Chris G. Van de Walle High doping concentrations can be achieved in tungsten trioxide (WO$_{3})$, which has an ABO$_{3}$ perovskite structure with an empty A site. Using firstprinciples calculations, we investigate the role of LO phonon scattering in electron transport. We use density functional theory to calculate electronic structure and vibrational spectra. Various approaches to electronphonon coupling are investigated, and the role of spinorbit splitting in the scattering mechanisms is examined. We compare WO$_{3}$ to other perovskites and find that the mobility of WO$_{3}$ is enhanced due to the absence of an Asite atom and the presence of spinorbit coupling. [Preview Abstract] 
Tuesday, March 14, 2017 3:06PM  3:42PM 
H8.00004: Thermal Transport in Thermoelectric Materials with Chemical Bond Hierarchy Invited Speaker: Wenqing Zhang Understanding thermal transport in complex materials is a critical issue in searching for highperformance thermoelectric materials. This talk will summarize our recent work on the diverse lattice dynamics and unusual thermal transport in compound materials with different level of structural complexity. Usually, the thermal transport is described by the traditional concept of “phonon” and phonon scattering anharmonicity. A concept of partcrystalline partliquid state (or liquidlike), and even partcrystalline partglass state (or glasslike), was demonstrated in some materials such as Cu$_{\mathrm{3}}$SbSe$_{\mathrm{3\thinspace }}$and Cu$_{\mathrm{2}}$(S,Se) with chemicalbond hierarchy, in which certain constituent species weakly bond to other part of the crystal. Those materials intrinsically manifest the coexistence of rigid crystalline sublattices and the other fluctuating noncrystalline sublattices with large atomic displacement amplitude and even flow of the subgroups of atoms. The largeamplitude vibrations and liquidlike flow of atoms generate unusual severe phonon scattering and thermal damping due to the collective lowfrequency vibrations similar to the Boson peak in amorphous or liquid materials, leading to the phenomenon of “phonon” scattering beyond the traditional anharmonicity. [Preview Abstract] 
Tuesday, March 14, 2017 3:42PM  3:54PM 
H8.00005: Vibrational properties and electronphonon coupling in Ga2O3 from first principles Emmanouil Kioupakis, Kelsey Mengle, Guangsha Shi $\beta $Ga2O3 is a wide bandgap semiconductor that is used in an increasing number of applications, such as power electronics and deepUV emission. One feature of this material is its low thermal conductivity, which although detrimental for power electronics, it may enable applications in thermoelectric devices. We investigated the vibrational and electronphonon coupling properties of Ga2O3 with firstprinciples calculations based on density functional theory, density functional perturbation theory, and the GW method. We will discuss calculated results for the phonon properties (frequencies, heat capacity, sound velocities, isotope effects), electronphonon coupling, and transport coefficients (Seebeck coefficient, electrical conductivity, and estimated electronic figure of merit ZTe). Our results demonstrate the applicability of $\beta $Ga2O3 for thermoelectric applications under appropriate doping and temperature conditions. This research was supported by the National Science Foundation through Grant No. DMR1534221 and the GRFP through Grant No. DGE 1256260. Computational resources were provided by the DOE NERSC facility under Contract No. DEAC0205CH11231 and by XSEDE, supported by NSF grant ACI1053575. [Preview Abstract] 
Tuesday, March 14, 2017 3:54PM  4:06PM 
H8.00006: Highfield Transport in Low Symmetry $\beta $Ga$_{\mathrm{2}}$O$_{\mathrm{3}}$ Crystal. Krishnendu Ghosh, Uttam Singisetti Highfield carrier transport plays an important role in many disciplines of electronics. Conventional transport theories work well on highsymmetry materials but lacks insight as the crystal symmetry goes down. Newly emerging materials, many of which possess low symmetry, demand more rigorous treatment of charge transport. We will present a comprehensive study of highfield transport using ab initio electronphonon interaction (EPI) elements in a fullband Monte Carlo (FBMC) algorithm. We use monoclinic $\beta $Ga$_{\mathrm{2}}$O$_{\mathrm{3}}$ as a benchmark lowsymmetry material which is also an emerging widebandgap semiconductor. $\beta $Ga$_{\mathrm{2}}$O$_{\mathrm{3\thinspace }}$has a C$_{\mathrm{2m}}$ space group and a 10 atom primitive cell. In this work the EPIs are calculated under densityfunctional perturbation theory framework. We will focus on the computational challenges arising from many phonon modes and low crystal symmetry. Significant insights will be presented on the details of energy relaxation by the hot electrons mediated by different phonon modes. We will also show the velocityfield curves of electrons in different crystal directions. [Preview Abstract] 
Tuesday, March 14, 2017 4:06PM  4:18PM 
H8.00007: Automated combinatorial method for fast and robust prediction of lattice thermal conductivity Jose J Plata, Pinku Nath, Demet Usanmaz, Cormac Toher, Marco Fornari, Marco Buongiorno Nardelli, Stefano Curtarolo The lack of computationally inexpensive and accurate {\it abinitio} based methodologies to predict lattice thermal conductivity, $\kappa_l$, without computing the anharmonic force constants or performing timeconsuming {\it abinitio} molecular dynamics, is one of the obstacles preventing the accelerated discovery of new high or low thermal conductivity materials. The Slack equation is the best alternative to other more expensive methodologies but is highly dependent on two variables: the acoustic Debye temperature, $\theta_a$, and the Gr\"{u}neisen parameter, $\gamma$. Furthermore, different definitions can be used for these two quantities depending on the model or approximation. Here, we present a combinatorial approach based on the quasiharmonic approximation to elucidate which definitions of both variables produce the best predictions of $\kappa_l$. A set of 42 compounds was used to test accuracy and robustness of all possible combinations. This approach is ideal for obtaining more accurate values than fast screening models based on the Debye model, while being significantly less expensive than methodologies that solve the Boltzmann transport equation. [Preview Abstract] 
Tuesday, March 14, 2017 4:18PM  4:30PM 
H8.00008: Thermoelectric properties of AMg$_{2}$X$_{2}$, AZn$_{2}$Sb$_{2}$ (A $=$ Ca, Sr, Ba; X $=$ Sb, Bi), and Ba$_{2}$ZnX$_{2}$ (X $=$ Sb, Bi) Zintl compounds. JIFENG SUN, David Singh A theoretical investigation of the electronic structure and transport properties of eleven Zintl compounds including nine 122 phases (AMg$_{2}$X$_{2}$, AZn$_{2}$Sb$_{2}$ (A $=$ Ca, Sr, Ba; X $=$ Sb, Bi)) and two 212 phases (Ba$_{2}$ZnX$_{2}$ (X $=$ Sb, Bi)) are reported. The electronic structures and electrical transport properties are studied using \textit{ab} initio calculations and semiclassical Boltzmann theory within the constant relaxation time approximation. Band structure calculations using mBJ potential with spinorbit coupling verify the semiconducting behavior for all of the compounds. The Seebeck coefficient, electrical conductivity and power factor results predict that the ntype 122 phase having better thermoelectric performance than ptype material due to the larger multivalley degeneracy at and near conduction band minimum compared with valence band maximum. The general performance of 212 phase is inferior to the 122 phase, with Ba$_{2}$ZnSb$_{2}$ compound showing better performance. The anisotropy character of Seebeck coefficients and electrical conductivity is also discussed. [Preview Abstract] 
Tuesday, March 14, 2017 4:30PM  4:42PM 
H8.00009: Exact Thermal Transport Properties of GrayArsenic using ElectonPhonon Coupling SeoungHun Kang, YoungKyun Kwon Using various theoretical methods, we investigate the thermoelectric property of gray arsenic. Thermoelectric devices that utilize the Seebeck effect convert heat flow into electrical energy. The conversion efficiency of such a device is determined by its figure of merit or $ZT$ value, which is related to various transport coefficients, such as Seebeck coefficient and the ratio of its electrical conductivity to its thermal counterpart for given temperature. To calculate various transport coefficients and thus the $ZT$ values of gray arsenic, we apply the Boltzmann transport theory to its electronic and phononic structures obtained by density functional theory and density functional perturbation theory together with maximally locallized Wannier functions. During this procedure, we evaluate its relaxation time accurately by explicitly considering electronphonon coupling. Our result reveals that gray arsenic may be used for a good $p$type thermoelectric devices. [Preview Abstract] 
Tuesday, March 14, 2017 4:42PM  4:54PM 
H8.00010: Giant phonon anharmonicity and thermal resistance from topological dispersion nesting in CuCl. Saikat Mukhopadhyay, Dipanshu Bansal, Olivier Delaire, Didier Perrodin, Edith BourretCourchesne, David Singh, Lucas Lindsay We report the phonon properties of zincblende CuCl, a very simple system with surprisingly rich anharmonic phonon physics, combining first principles calculations with inelastic neutron scattering measurements. We find a new quasiparticle peak in the phonon density of states emerging with increasing temperature. This peak arises from nesting of numerous offresonance modes with highly asymmetric line shapes providing large phase space for both coalescence and decay processes involving longitudinal acoustic, transverse acoustic and transverse optic modes throughout the Brillouin zone. We further correlate this strong anharmonicity in CuCl to its nonmonotonic pressure dependent thermal conductivity behavior via a balance of increasing group velocities and scattering rates of longitudinal acoustic modes, challenging the existing theory. [Preview Abstract] 
Tuesday, March 14, 2017 4:54PM  5:06PM 
H8.00011: Explanation of the Electronic Transition in ZrTe$_5$ and HfTe$_5$ David J Singh, Jinguang Cheng The pentatellurides, ZrTe$_5$ and HfTe$_5$ show strong electronic transitions at 150 K and 70 K, for the two compounds, respectively. This is seen in a strong resistivity peak and a sign change from a large electronlike to a large holelike thermopower. This is not associated with a structural transition. Here use transport theory and the first principles band structure to show the origin of the transition in the particular electronic structure of these compounds. Results in good accord with experiment are found both for the transition temperatures and the effects in transport. [Preview Abstract] 
Tuesday, March 14, 2017 5:06PM  5:18PM 
H8.00012: Theory of Thermal Conductivity of Thermoelectric Clathrates above the Plateau Qing Xi, Jun Zhou, Tsuneyoshi Nakayama, Baowen Li 
Tuesday, March 14, 2017 5:18PM  5:30PM 
H8.00013: Abstract Withdrawn Thermoelectric (TE) power is generated by utilizing a temperature differential created across a material. Such energy conversion takes place without the incorporation of any moving part and can often lead to substantial recovery of waste heat into useful electrical energy. Ceramic oxides have gained attention as a new class of TE materials because of their high stability at elevated temperatures, where higher conversion efficiencies are expected. The present investigation uses Barium plumbate (BaPbO$_{\mathrm{3}})$ as the starting material, the TE properties of which have been altered by reasonable cation substitutions. As BaPbO$_{\mathrm{3}}$ has high electrical conductivity, $\sigma $\textasciitilde 1.1x10$^{\mathrm{5}}\Omega ^{\mathrm{1}}$m$^{\mathrm{1}}$at room temperature, its thermopower, $S$, is relatively low 21$\mu $V/K. With a thermal conductivity, $k$, of \textasciitilde 3.00W/m.K, the figure of merit (\textit{ZT}$=S^{\mathrm{2}}\sigma $\textit{Tk}$^{1})$ of BaPbO$_{\mathrm{3\thinspace }}$is \textasciitilde 0.01 at $T=$300$K$. BaPbO$_{\mathrm{3\thinspace }}$is a prospective TE material because it exhibits high electrical conductivity like metals. However, it exhibits remarkably low thermal conductivity, which renders it attractive TE qualities. The open perovskite structure of BaPbO$_{\mathrm{3\thinspace }}$allows it to accommodate a large variety of dopants in relatively large concentrations. This work investigates the variation of TE properties of BaPbO$_{\mathrm{3\thinspace }}$as Ba ions are systematically substituted by other cations. 
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