Bulletin of the American Physical Society
APS March Meeting 2020
Volume 65, Number 1
Monday–Friday, March 2–6, 2020; Denver, Colorado
Session S44: Electrons, Phonons, Electron Phonon Scattering, and Phononics VFocus

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Sponsoring Units: DCOMP DMP Chair: Xiulin Ruan, Purdue University Room: 704 
Thursday, March 5, 2020 11:15AM  11:51AM 
S44.00001: Characterization of Thermal Effects in Wide Bandgap Semiconductor Materials and Devices Invited Speaker: Samuel Graham Wide bandgap electronics made from nitrides (e.g., Gallium Nitride (GaN)) and oxides (e.g., Gallium Oxide (Ga_{2}O_{3})) are currently under development due to their potential to create some of the most advanced RF and power electronic devices in the world. However, the thermal response of these devices under applied electric fields can create large power densities (RF and power electronics) that must be understood. For many of these devices, the electrothermal response plays a strong role in both the acceptable operation or longterm failure and reliability of the devices. Thus, tools that can help elucidate these responses and provide a method to help design better devices is of critical need for this field. 
Thursday, March 5, 2020 11:51AM  12:03PM 
S44.00002: Direct solution to the spacetime dependent PeierlsBoltzmann transport equation using an eigendecomposition method Chengyun Hua Nonlocal thermal transport is generally described by the PeierlsBoltzmann transport equation (PBE). However, solving the PBE for a general spacetime dependent problem remains a challenging task due to the high dimensionality of the integrodifferential equation. In this work, we present a direct solution to the spacetime dependent PBE with a linearized collision matrix using an eigendecomposition method. Furthermore, we show that there exists a generalized Fourier type relation that links heat flux to the local temperature, and this constitutive relation is valid from ballistic to diffusive regimes. Combining this approach with ab initio calculations of phonon properties, we demonstrate that the derived solution gives a more accurate description of thermal transport in crystals that exhibit weak anharmonicity than the commonlyused singlemode relaxation time approximation and thus will lead to an improved understanding of phonon transport in solids. 
Thursday, March 5, 2020 12:03PM  12:15PM 
S44.00003: Calculation of mode Gruneisen parameters made simple Angelo Bongiorno Gruneisen parameters measure the degree of anharmonicicy of a material. 
Thursday, March 5, 2020 12:15PM  12:27PM 
S44.00004: Density functional perturbation theory for lattice dynamics with fully relativistic ultrasoft pseudopotentials: the magnetic case Andrea Urru, Andrea Dal Corso We discuss the extension of density functional perturbation theory for lattice 
Thursday, March 5, 2020 12:27PM  12:39PM 
S44.00005: Photothermal imaging as a new tool for the investigation of the temperaturedependent properties of the medium in nanoscale Maryam Zahedian, Bogdan Dragnea Photothermal imaging is a powerful technique to detect small lightabsorbing nanoparticles down to 1.4 nm with a high spatial resolution (1). The signal magnitude is proportional to the absorption crosssection of the nanoparticle as well as properties of the medium. Finite thermal diffusivity of the medium causes a phase delay in the response of the heat dissipation. The phase delay at each point integrated over the resolution disk is identified as the photothermal signal phase that depends on the material property (2). In this study, first, we demonstrate that the photothermal phase is capable of monitoring the local medium modifications, with high sensitivity. Second, we determine that, with the aid of simulation, information about the temperaturedependent properties of the medium, such as heat conductivity is attainable in nanoscale. 
Thursday, March 5, 2020 12:39PM  12:51PM 
S44.00006: Thermal Transport in Phosphorene Guangzhao Qin, Zhenzhen Qin Phosphorene, a novel elemental 2D semiconductor, possesses fascinating chemical and physical properties which are distinctively different from other 2D materials. The rapidly growing applications of phosphorene in nano/optoelectronics and thermoelectrics call for comprehensive studies of the thermal transport properties. In this talk, based on the theoretical and experimental progresses, the thermal transport properties of singlelayer phosphorene, multilayer phosphorene (nanofilms), and bulk black phosphorus are summarized to give a general view of the overall thermal conductivity trend from singlelayer to bulk form. The mechanism underlying the discrepancy in the reported thermal conductivity of phosphorene is discussed by reviewing the effect of different functionals and cutoff distances on the thermal transport evaluations. This review then provides fundamental insight into the thermal transport in phosphorene by reviewing the role of resonant bonding in driving giant phonon anharmonicity and longrange interactions. In addition, the extrinsic thermal conductivity of phosphorene is reviewed by discussing the effects of strain and substrate, together with phosphorene based heterostructures and nanoribbons. 
Thursday, March 5, 2020 12:51PM  1:03PM 
S44.00007: Thermoelectric properties of halfHeusler TaFeSb from firstprinciples electronphonon scattering calculations Natalya Fedorova, Andrea Cepellotti, Boris Kozinsky We investigate thermoelectrics transport properties of halfHeusler TaFeSb within the Boltzmann transport formalism, using first principles calculations of the electronic relaxation times. Our goal is to explore the microscopic origin of exceptionally high ZT values (up to 1.52 at 973 K) recently reported from the experimental measurements of transport properties of TaFeSbbased compounds. In particular, we focus on the effects arising from the electronphonon interaction. For that we calculate corresponding scattering rates using WannierFourier interpolation of electronphonon matrix elements as well as the recently developed electronphonon averaged (EPA) approximation. We discuss the likely mechanisms of high ZT in TaFeSbbased systems and possible ways to further improve thermoelectric properties of halfHeusler compounds. 
Thursday, March 5, 2020 1:03PM  1:15PM 
S44.00008: Thermal phonons with micronscale mean free paths in ultradrawn polyethylene Taeyong Kim, Stavros X. Drakopoulos, Ignacio MartinFabiani, Andrew Robbins, Sarah Ronca, Austin Minnich Heat conduction in highly oriented polymers is of fundamental and practical interest. It is wellknown that the thermal conductivity of certain polymers such as polyethylene (PE) increases by orders of magnitude with drawing, but the microscopic properties of phonons responsible for heat conduction have remained difficult to access experimentally. Here, we report the observation of thermal phonons with micronscale mean free paths (MFPs) in ultradrawn polyethylene using transient grating spectroscopy. The MFPs are comparable to those in covalent single crystals such as Si despite the imperfect nature of the sample’s microstructure. Further, the sample exhibits a decrease in thermal conductivity with increasing temperature above 200 K, indicating that anharmonic scattering is dominant over reflections from domains between crystallites. Our work provides new insights into the microscopic origin of high uniaxial thermal conductivity of ultradrawn polymers. 
Thursday, March 5, 2020 1:15PM  1:27PM 
S44.00009: Accelerated Screening of ElectronPhonon Transport in 2D Materials Jennifer Coulter, Boris Kozinsky Numerous experimental and theoretical studies have identified promising 2D materials for thermoelectric applications. These materials can exhibit an advantageous combination of electrical and thermal properties, sometimes resulting in large thermoelectric figureofmerit values. Using an inhouse method to perform accelerated screening of transport properties through firstprinciples electronphonon calculations, we consider thermoelectric effects in a broader set of 2D materials. From these calculations, we consider how specific electronic and vibrational properties relate to thermoelectric potential, and identify the best candidate materials for use in application. Additionally, we consider the practical importance of substrate effects on the electronphonon interaction and transport properties of these materials. 
Thursday, March 5, 2020 1:27PM  1:39PM 
S44.00010: Simulations of thermoelectric coefficients using DFT bandstructures and energy dependent scattering rates Patrizio Graziosi, Chathurangi Kumarasinghe, Neophytos Neophytou Performance prediction for thermoelectric (TE) materials requires extracting DFT bandstructures and computation of TE coefficients using Boltzmann transport equation (BTE). The constant relaxation time approximation is commonly employed due to complexities in accurately computing scattering rates. 
Thursday, March 5, 2020 1:39PM  1:51PM 
S44.00011: ZeroPoint renormalization of the band structure within Quasiparticle Selfconsistent GW Savio Laricchia, Nicola Bonini, Mark van Schilfgaarde The reliability of Density Functional Theory (DFT) for the electronphonon coupling in many materials, including even simple spbonded compounds, has been questioned in recent years. Hybrid functionals and quasiparticle GW corrections suggest that nonlocal exchangecorrelation enhances the electronphonon interaction as a consequence of an improved description of the electronic screening. This has highlighted the need to move beyond local exchangecorrelation functionals within DFT, but complete fieldtheoretic investigations are still missing in literature. In this talk I will introduce the development of a fieldtheoretic methodology which is able to predict on an equal footing electronic quasiparticles and phonons as well as their interaction. Such an approach has been implemented within the Quasiparticle Selfconsistent GW (QSGW) formalism which describes well the electronic properties for a wide range of materials, including many where standard DFT fails. The reliability of a such fieldtheoretic methodology will be discussed with applications ranging from the renormalization of the optical gap of nonpolar semiconductors to the renormalization of the Fermi surface of correlated materials such as FeSe. 
Thursday, March 5, 2020 1:51PM  2:03PM 
S44.00012: PhononPhonon Quantum Coherent Coupling in GaAs/AlAs Superlattice Feng He, Nathanial Sheehan, Xianghai Meng, Seth Bank, Raymond Orbach, Yaguo Wang Quantum coherent coupling between a zonecenter phonon and two acoustic phonons was observed in two GaAs/AlAs superlattices (8 nm/8 nm and 5.4 nm/5.4 nm) at ambient temperature. Using degenerate coherent phonon spectroscopy, a multicycle oscillation feature appears in the timeresolved phonon amplitudes of both samples, as a result of the coherent energy exchange between a driving phonon mode near first Brillouin zone center and two target acoustic phonon modes. This feature resembles the photon resonant parametric down/upconversion processes, as well as the reversible coherent energy exchange between the optical field and a mechanical oscillator, suggesting quantum coherent coupling between the driving and target phonon modes. In the 8nm/8 nmsuperlattice, the coupling strength increases nonlinearly at high pump fluences, which may eventually reach an extreme state where all three phonon modes share the same coherent state, as predicted by Orbach in the 1960’s. 
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