Bulletin of the American Physical Society
APS March Meeting 2022
Volume 67, Number 3
Monday–Friday, March 14–18, 2022; Chicago
Session S48: Electrons, Phonons, ElectronPhonon Scattering, and Phononics VFocus Recordings Available

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Sponsoring Units: DCOMP DMP Chair: Chris Marianetti, Columbia University Room: McCormick Place W471A 
Thursday, March 17, 2022 8:00AM  8:12AM 
S48.00001: Firstprinciples calculation of thermomagnetic transport effects Jennifer Coulter, Andrea Cepellotti, Boris Kozinsky As the need for energyefficient devices has become more pressing, so has interest in finding ways to enhance the thermoelectric performance of materials. While the Seebeck effect has been intensely studied, thermomagnetic transport has rarely seen computational investigation. Recent results, such as those showing enhanced thermopower in compensated semimetals via the Nernst effect, suggest that it also has potential to provide enhancements in thermoelectric performance in the right circumstances. Additionally, established results such as those for bismuth and graphite, which show lowtemperature peaks in the Nernst coefficient, could be better understood or further engineered for potential applications. However, these interesting and possibly useful behaviors can be difficult to interpret from experimental results alone. Using firstprinciples solutions of the Boltzmann transport equation as implemented in our new opensource code package Phoebe [1], we calculate the Seebeck and Nernst coefficients to better understand the physics underlying these effects. 
Thursday, March 17, 2022 8:12AM  8:24AM 
S48.00002: Thermodynamic explanation of the Invar effect by computation and experiments Stefan Haegeli Lohaus, Matthew Heine, Pedro Guzman, Camille M Bernal, Olle Hellman, David A Broido, Brent T Fultz Phonons, electrons, spins and their interactions give the entropy and free energy of magnetic materials. A Maxwell relation implies that the pressure dependence of these entropy contributions must somehow sum to zero, to give Invar materials their known zero thermal expansion. With experiments and computations, we evaluated these thermodynamic contributions from lattice vibrations and spin disorder versus pressure for Fe36%Ni Invar. From nuclear resonant inelastic Xray scattering and Mössbauer spectroscopy at varying temperatures and pressures, we measured the phonon density of states and the magnetization, and determined their individual contributions to the entropy of Invar. Calculations of the phonon modes performed with an ab initio effective potential method that includes the magnetic disorder are able to capture the anomalies in the thermal expansion, and are in good agreement with experiments. The low thermal expansion of Invar is explained by the cancellation of entropy effects from lattice vibrations and spin disordering. 
Thursday, March 17, 2022 8:24AM  8:36AM 
S48.00003: Quasiparticle dispersion of a 2D layer of BaBiO3 Stepan Fomichev, Mona I Berciu We use the Momentum Average approximation to find the spectral function of the quasiparticle that forms when a hole is doped into a parent layer of BaBiO3. To model this system, we include the 6s Bi and the p_x/y O ligand orbitals, and treat the phonons as dispersionless, quantum Einstein modes on the oxygens only. The holephonon coupling is of Peierls/SSH origin, arising from the changes in the sp and pp hopping amplitudes due to oxygen displacements. In the undoped ground state, this electronphonon coupling is responsible for driving a breathingmode distortion of the O octahedra, leading to insulating behavior. Our calculation investigates how this distortion is modified in the vicinity of the quasiparticle, as the doped hole acquires its own phonon cloud. We also calculate the spectral function for two doped holes, to study the possibility of bipolaron formation. A stable bipolaron could provide a direct explanation for the relatively high T_c observed in the superconducting bismuthates. 
Thursday, March 17, 2022 8:36AM  9:12AM 
S48.00004: Froehlich condensate of Phonons and heat control Invited Speaker: Baowen Li Different from BoseEinstein Condensate (BEC) that occurs at equilibrium, phonon condensate happens in the condition of out of equilibrium[1]. In this work, we will present that the Fröhlich condensate of phonons can be realized in optomechanical systems [2] as well as in a selffeedback classical mechanical system [3]. Our optomechanical system consists of a onedimensional array of membranes coupled to the cavity field via a quadratic interaction, and the cavity is pumped by an external laser. Analytical and numerical results demonstrate that the high phonon occupancy of the lowest or highest mechanical mode is achievable depending on the detuning of the driving laser, the optomechanical strength, and the temperature. The feasibility of experimental implementation is discussed. Our results shed light on energy conversion and transfer, heat control, and multimode cooling using optomechanical systems. 
Thursday, March 17, 2022 9:12AM  9:24AM 
S48.00005: Coherent state representation of lattice vibrations and its application to electronphonon interaction Donghwan Kim Since the introduction of the deformation potential model to describe electronphonon interaction, the mechanism of the scattering of the electron by the lattice vibrations was described by phonon creation and annihilation using second quantization for the lattice vibrations. Furthermore, an incoherent concatenation of firstorder scattering events using Boltzmann transport theory was used to calculate resistivity. 
Thursday, March 17, 2022 9:24AM  9:36AM 
S48.00006: Identifying thermal insulators via ab initio Green Kubo simulations guided by anharmonicity Florian Knoop, Matthias Scheffler, Christian Carbogno We present a systematic firstprinciples search for thermal insulators in material space, covering hundreds of compounds, five lattice types and seven space groups, including simple rocksalt and zinc blende structures up to complex perovskites with 20 atoms per unit cell. Using the highthroughput framework FHIvibes [1,2] and a recently developed measure for the strength of anharmonicity [3], we identify 120 candidate materials with potential for ultralow thermal conductivity <2 W/mK at room temperature, i.e., comparable to those of thermoelectrics such as SnSe or MgSb. We perform nonperturbative ab initio GreenKubo simulations [4] for the 60 most promising candidates, thereby including all anharmonic effects responsible for low thermal conductivity. 
Thursday, March 17, 2022 9:36AM  9:48AM 
S48.00007: Symmetrybased lattice dynamics and thermal transport in magnetic CrCl_{3} and RuCl_{3} Xun Li, Lucas Lindsay, Sai Mu, Tom Berlijn The primitive WignerSeitz cell, and corresponding first Brillouin zone (FBZ), is typically used for calculations of lattice vibrational properties as it contains the smallest number of degrees of freedom and thus has cheapest computational cost. However, in complex materials, the FBZ can take on irregular shapes where lattice symmetries are not apparent. Thus conventional cells (with more atoms and regular shape) are often used to describe materials, though dynamical calculations are more expensive. Here we discuss mapping of conventional cell dynamics to primitive cell dynamics based on translational symmetries and phases. This leads to phase interference conditions that act like conserved quantum numbers that enable a conventional cell description of vibrations and transport at nearly the same computational cost as those done in the primitive cell. We demonstrate this dynamics using first principles calculations to simulate phonons in two technologicallyrelevant magnetic systems: the cleavable antiferromagnet CrCl_{3} and the quantum spin liquid candidate aRuCl_{3}. Additionally, stacking fault limited, low temperature phonon transport in aRuCl_{3} is examined with regards to measured data, thus providing physical insights into thermal Hall behaviors of Kitaev spinliquid materials. 
Thursday, March 17, 2022 9:48AM  10:00AM 
S48.00008: Theory of dynamical structure factors in complex twisted materials Lucas Lindsay, Rinkle Juneja, Simon Thebaud, Tribhuwan Pandey, Carlos A Polanco, Duncan Moseley, Michael E Manley, Yongqiang Cheng, Barry Winn, Douglas L Abernathy, Raphael P Hermann Structural complexity underlies a variety of novel quasiparticle behaviors that can have profound impacts on material functionalities. Here we intimately examine the theory of lattice dynamical spectra of ‘twisted’ materials with combined rotational and translational symmetries. We advance a dynamical theory that incorporates the twist symmetry directly into the description of the phonon frequencies and eigenvectors, which naturally elucidates the underlying angular momenta of phonon bands. We apply this theory to build insights into dynamical structure factors and spectral observations from inelastic neutron and xray scattering experiments. 
Thursday, March 17, 2022 10:00AM  10:12AM 
S48.00009: The quasiharmonic approximation via space group irreducible derivatives Mark Mathis, Lyuwen Fu, Chris Marianetti The quasiharmonic approximation (QHA) is the simplest nontrivial approximation for interacting phonons under constant pressure, bringing the effects of anharmonicity into temperature dependent observables. Nonetheless, the most general version of the QHA is often implemented with additional approximations due to the complexity of computing phonons under arbitrary strains. Here we circumvent the aforementioned complexity by employing irreducible second order displacement derivatives of the BornOppenheimer potential and their strain dependence, which are efficiently and precisely computed using the lone irreducible derivative approach. We execute two complementary strain parametrizations: a discretized strain grid interpolation and a Taylor series expansion in symmetrized strain. We illustrate our approach by evaluating the thermal expansion and temperature dependence of the elastic constant tensor in thoria and lead titanate using density functional theory, and compare to experimental measurements. Our irreducible derivative approach to the QHA will facilitate reproducible, high throughput applications. 
Thursday, March 17, 2022 10:12AM  10:24AM 
S48.00010: Topological Invariant of Acoustic Phonons in 2D materials Gunnar F Lange, Adrien Bouhon, Bartomeu Monserrat, RobertJan Slager

Thursday, March 17, 2022 10:24AM  10:36AM 
S48.00011: Extremely high thermoelectric performance of SnSe at optimal carrier densities Anderson S Chaves, Daniel T Larson, Efthimios Kaxiras, Alex Antonelli Highefficiency thermoelectric materials are desirable for their capability of functioning as all solidstate modules for electric power generation from waste heat or distributed spotsize refrigeration. Bulk tin selenide (SnSe) has received much attention since its excellent thermoelectric figure of merit (zT) was reported. Using extensive firstprinciples calculations of carrierimpurity and carrierphonon scattering processes, we investigate the optimal carrier densities to maximize zT in p and ndoped SnSe over a broad range of temperatures. We predict an ultrahigh zT > 4 for inplane pdoped and outofplane ndoped SnSe at high temperatures, which is robust against variations in the concentration of ionized impurities. An extensive analysis of the transport properties as a function of the carrier density and temperature indicates that the Lorenz number reaches a minimum at the optimal conditions. Our results are motivation for improving the efficiency of doping in SnSe in order to attain optimal carrier densities. 
Thursday, March 17, 2022 10:36AM  10:48AM 
S48.00012: Selfconsistent extended Hubbard functional study on electronic and structural properties of BaBiO_{3} and BaSbO_{3} Bo Gyu Jang, Minjae Kim, SangHoon Lee, Wooil Yang, SeungHoon Jhi, YoungWoo Son Ba_{1x}K_{x}BiO_{3 }(BKBO) has long been a subject of great interest due to its intertwined electronic and structural properties. Recently, comparative material Ba_{1x}K_{x}SbO_{3 }(BKSO) is also successfully synthesized and exhibits a similar phase diagram with BKBO. It is well established that the simple DFT fails to describe several physical properties of BKBO compound while the hybrid functional or GW methods are better in many aspects although comprehensive studies for its entire phase diagram are limited due to their expensive computational cost. Here, based on a newly developed ab initio method counting selfconsistent on and intersite Coulomb interactions, we examine the electronic, structural, and phonon properties of BKBO and BKSO with various potassium doping levels. Our new method can describe the bandgaps and phonon dispersions of semiconductors precisely in a similar level to the GW method, but at the simple DFT computational cost. We found that the new method gives much improved results compared to the simple DFT calculations. A comprehensive comparative study on the electronic and structural properties of BKBO and BKSO will be discussed. 
Thursday, March 17, 2022 10:48AM  11:00AM 
S48.00013: Thermoelectric properties and carrier dynamics in twodimensional chalcogenides Raveena Gupta, Chandan Bera In recent years, 2D layered metal chalcogenides and transition metal dichalcogenides (TMDs) have received tremendous attention due to their unique electronic, thermal and optoelectronic properties leading to their applications in optoelectronics and thermoelectrics (TE).[1,2] Understanding of electron and phonon scattering mechanisms and carrier dynamics is critical for optimization of the transport properties in new devices. TMDs like MoS_{2}, MoSe_{2} and WS_{2} are being investigated because of the electronic, optical and spin properties exhibited by them as they go from bulk to monolayer. The TE properties of few layers and monolayer TMDs are of great interest due to low thermal conductivity and increased power factor. In this context, we use the Boltzmann transport formalism to assess the potential of monolayer and bilayer TMDs and monolayer metal chalcogenide[3] as TE material by employing different electron and phonon scattering mechanisms. Carrier dynamics is also studied to understand the device efficiency. 
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