Bulletin of the American Physical Society
APS March Meeting 2022
Volume 67, Number 3
Monday–Friday, March 14–18, 2022; Chicago
Session G48: Electrons, Phonons, ElectronPhonon Scattering, and Phononics IIFocus Recordings Available

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Sponsoring Units: DCOMP DMP Chair: Feliciano Giustino, University of Texas Room: McCormick Place W471A 
Tuesday, March 15, 2022 11:30AM  12:06PM 
G48.00001: Modeling superconducting properties with the Eliashberg formalism Invited Speaker: Elena R Margine Ab initio prediction of superconducting properties remains among the most challenging problems in materials research. Recent advances in computational methodology based on the Eliashberg formalism represent an important milestone in moving toward fully ab initio description of phononmediated superconductors. In this talk, I will introduce our computational framework that combines the fully anisotropic Eliashberg theory with electronphonon interpolation based on maximallylocalized Wannier functions. The methodology, implemented in the opensource EPW package, allows one to perform highly accurate calculations of the anisotropic temperaturedependent superconducting gap and critical temperature. I will illustrate the performance of this advanced computational technique on several prototypical systems. 
Tuesday, March 15, 2022 12:06PM  12:18PM 
G48.00002: Electronphonon scattering in monolayer MoS2: Multiscale machine learned deformation potential approach Ransell DSouza, Stephen Fahy, Ivana Savic

Tuesday, March 15, 2022 12:18PM  12:30PM 
G48.00003: elphbolt: An ab initio solver for the coupled and decoupled electron and phonon Boltzmann transport equations Nakib H Protik, Chunhua Li, Miguel A Pruneda, David A Broido, Pablo Ordejon Calculation of the electronphonon (eph) drag effect requires addressing the selfconsistent transport of both these species. Here we present elphbolt [1]  a free/libre software for solving both the coupled and decoupled e and ph Boltzmann transport equations. This software allows the efficient calculation of the effect of the mutual eph drag on the thermal and charge conductivities, and the thermopower. The code uses ab initio eph and phph couplings and employs a novel iterative procedure that enforces the KelvinOnsager relationship between the Seebeck and the Peltier thermopowers, as mandated by thermodynamics. The code also takes advantage of the coarray feature of modern Fortran, which provides convenient native syntax for parallelization. In this talk, we highlight the design and capabilities of the code with examples. The code is hosted at https://github.com/nakib/elphbolt. [1] Protik, N. H., Li, C., Pruneda, M., Broido, D. and Ordejón, P., 2021. elphbolt: An ab initio solver for the coupled electronphonon Boltzmann transport equations. arXiv preprint arXiv:2109.08547. 
Tuesday, March 15, 2022 12:30PM  12:42PM 
G48.00004: Firstprinciples study of highfield charge transport and fluctuations in nGaAs Austin J Minnich, Alexander Y Choi, ShiNing Sun Firstprinciples calculations of charge transport properties in semiconductors are now routine but typically restricted to low field, linear response properties such as mobility. On the other hand, the power spectral density (PSD) is known to be sensitive to the precise electronphonon interactions occurring in the material and is readily experimentally accessible, yet few abinitio calculations of this quantity have been reported. Here, we report an abinitio calculation of both high field transport properties and power spectral density (PSD) of hot electrons in GaAs. We find that although qualitative agreement is observed for the highfield drift velocity characteristics, the agreement with the PSD is poor. The agreement for the drift velocity is improved with inclusion of onshell twophonon processes but fails to improve the agreement with the PSD. Our work suggests that additional scattering processes are of fundamental importance to explain the PSD trend with electric field in GaAs. Further, our work illustrates the use of PSD to probe the electronphonon interaction in semiconductors. 
Tuesday, March 15, 2022 12:42PM  12:54PM 
G48.00005: Ab initio theory of coherent electronphononphoton processes in photoemission from singlecrystal materials Johannes Kevin Nangoi, Siddharth Karkare, Ravishankar Sundararaman, Howard A Padmore, Tomás A Arias Perhaps surprisingly, in photoemission from some singlecrystal materials, coherent threebody electronphononphoton processes can dominate over twobody electronphoton processes. We present a fully ab initio theory of such processes including electronphonon matrix elements computed using Wannier function techniques and including electron emission process from bulk into vacuum. Our results explain why the momentum spread observed experimentally for photoelectrons from PbTe(111) differs from the expectations of previous theories by over an order of magnitude, and also predict that coherent electronphononphoton processes can contribute up to ~60% of the photocurrent from the emitted bulk electrons. Finally, we shall discuss the prospects for incorporating surface photoemission effects through a novel planewave Green’s function approach. 
Tuesday, March 15, 2022 12:54PM  1:06PM 
G48.00006: ElectronPhonon Scattering and Mobility in Atomically Thin AlN/GaN Superlattices from First Principles Nick Pant, Woncheol Lee, Nocona Sanders, Emmanouil Kioupakis Alloy scattering is stronger than electronphonon scattering in random AlGaN alloys, resulting in poor mobility compared to the ideal "virtual" alloys of GaN and AlN. In this work, we investigate the phononlimited electron mobility of atomically thin AlN/GaN superlattices using densityfunctional perturbation theory and manybody perturbation theory. The superlattices exhibit increased electron mobility and powerelectronics figure of merit compared to random AlGaN alloys due to the absence of alloy scattering. Although random alloys are poorly described by virtual crystals, we find that key transportrelated properties of the atomically thin superlattices are accurately described by a compositiondependent linear interpolation of the end binary compounds. Therefore, the replacement of a random solid solution with an atomically thin superlattice could be a general strategy for increasing the mobility of compounds for which alloy scattering dominates electronphonon scattering. 
Tuesday, March 15, 2022 1:06PM  1:18PM 
G48.00007: Coupled electronphonon transport from first principles Chunhua Li, Nakib H Protik, Pablo Ordejon, David A Broido The development of predictive theoretical descriptions of coupled charge and heat conduction in solids is essential to our fundamental understanding of the underlying microscopic processes controlling the transport phenomena. Here, we discuss our first principles theoretical/computational approach to exploring the regime in crystalline materials where the mutual interactions between electrons and phonons dominate thermoelectric transport behavior. Calculations are performed using the elphbolt code [1]. Results for selected materials will be presented. 
Tuesday, March 15, 2022 1:18PM  1:30PM 
G48.00008: Electron phonon coupling and coherent phonon modulation of charge transfer in two dimensional perovskite (AE2T)_{2}AgBiI_{8} Xixi Qin, Dovletgeldi Seyitliyev, Manoj K Jana, Svenja M Janke, Wei You, David B Mitzi, Kenan Gundogdu, Volker Blum Twodimensional (2D) hybrid organic inorganic perovskites (HOIPs) possess quantumwelllike atomic structures with alternating organic and inorganic layers, and exhibit wellseparated organic and inorganic energy levels near the band edges. The 2D HOIP (AE2T)_{2}AgBiI_{8} (AE2T: 5,5'diylbis(aminoethyl)(2,2'biothiophene)) has a type 2B electronic structure in which the valence band maximum (VBM) dominated by the organic components, lies in close proximity to the highest occupied inorganicderived states. Here, we show how electronphonon coupling effects can modulate the inorganic and organic derived band levels, which may induce charge transfer between organic and inorganic components. Transient absorption spectra (TAS) measured for (AE2T)_{2}AgBiI_{8} shows a carrier population oscillation at ~114 cm^{1}. Electron phonon coupling effect calculations for 48 phonon modes from 95 to 125 cm^{1} show that electron phonon coupling strength has a single largest peak near 115 cm^{1}, very close to the observed TAS oscillation frequency. We thus demonstrated a striking example of how electronphonon interactions can be used to manipulate important charge and energy transfer processes in 2D HOIPs. 
Tuesday, March 15, 2022 1:30PM  1:42PM 
G48.00009: Designing thermoelectric materials using interband electronphonon scattering anomalies. Jackson Weaver, Jennifer Coulter, Boris Kozinsky, Andrea Cepellotti In recent years, efforts have intensified in looking at alternative paradigms and design strategies for discovering efficient thermoelectric materials, which can be used to capture waste heat as electrical energy. In a recent work [1], we found that interband electronphonon scattering, that can occur in materials with intersecting heavy and light electron bands, leads to a strong variation of scattering lifetimes as a function of electron energy and can result in enhanced thermoelectric performance. When such a material is doped so that the chemical potential is near the heavy band, an anomalous peak in the thermoelectric power factor is observed. In this work, we perform a broad search for materials with such band characteristics. We performed detailed firstprinciples electronphonon transport calculations for several candidate materials to investigate the potential for increased thermoelectric performance based on this lightheavy band mechanism. 
Tuesday, March 15, 2022 1:42PM  1:54PM 
G48.00010: Electronphonon interactionin molecules and solidsusing hybrid functionals Han Yang, Arpan Kundu, Marco Govoni, Giulia Galli Accurate predictions of the electronic structure of molecules and solids, especially those containing light elements, rely on the ability to compute electronphonon interaction. We present a method to evaluate electronphonon interaction in electronic structure calculations carried out with hybrid functionals. We build on recent algorithms [1,2] that efficiently combine the calculations of electronelectron and electronphonon interaction, and we use density matrix perturbation theory. The implementation of the algorithm developed here is a part of the WEST code (http://www.westcode.org). We discuss verification and validation protocols and applications to both molecules and solids. 
Tuesday, March 15, 2022 1:54PM  2:06PM 
G48.00011: Band gap renormalization in 2D materials from firstprinciples Sahar Sharifzadeh The incorporation of electronphonon interactions in the modeling of materials is important for an accurate comparison of observables to experimental measurements. Optical and transport properties of materials are often strongly affected by the quantummechanical nature of lattice vibrations, which are quite expensive to incorporate explicitly in a firstprinciples approach. Here, using the special displacement (SD) method developed by Zacharias and Giustino [1], we study bandgap renormalization due to electronphonon coupling in 2D materials in a highthroughput fashion. For ~100 monolayer materials, we compute the gap with and without the presence of phonons within density functional theory and the SD approach. We parametrize the renormalization as a way to bridge the gap between computationally intensive firstprinciples calculations and phenomenological models of the temperature dependence of the band gap of materials. The connection between different physical descriptors of materials with band gap renormalization are explored and highlighted using a datadriven approach. 
Tuesday, March 15, 2022 2:06PM  2:18PM 
G48.00012: Lattice dynamics effects on magnetocrystalline anisotropy energy of YCo_{5} from first principles Guangzong Xing, Yoshio Miura, Terumasa Tadano YCo_{5} has attracted much attention due to its large magnetocrystalline anisotropy (MCA) energy, which decays as the temperature increases. So far, the origin of the temperature decay has been attributed solely to the spin fluctuation [1]. At elevated temperatures, however, the thermal excitation of phonons is expected to influence the MCA energy significantly, as in the case of MnBi [2]. 
Tuesday, March 15, 2022 2:18PM  2:30PM 
G48.00013: Efficient transport calculations in 2D materials Samuel Ponce, Miquel Royo, Marco Gibertini, Massimiliano Stengel, Nicola Marzari In this talk, we will extend the ab initio calculations of drift and Hall carrier mobilities in bulk materials [1] to the realm of 2D materials, relying on exact 2D electrostatic [2]. 
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