Bulletin of the American Physical Society
APS March Meeting 2022
Volume 67, Number 3
Monday–Friday, March 14–18, 2022; Chicago
Session F48: Electrons, Phonons, ElectronPhonon Scattering, and Phononics IFocus Recordings Available

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Sponsoring Units: DCOMP DMP Chair: E.R. Margine, SUNY Binghampton Room: McCormick Place W471A 
Tuesday, March 15, 2022 8:00AM  8:36AM 
F48.00001: Progress in ab initio calculations of polarons: reduced dimensionality and manybody effects Invited Speaker: Feliciano Giustino Polarons are among the most wellknown quasiparticles in solid state physics, and play an important role in the electronic, optical, and transport properties of many classes of materials, from organics to oxides. Recently we introduced an ab initio formalism to investigate small and large polarons on the same footing [1,2]. This formalism does not suffer from the delocalization error introduced by selfinteraction in density functional theory, and employs densityfunctional perturbation theory to circumvent the need for large supercell calculations. In this talk I will describe further progress on our ab initio theory of polarons on two fronts. Firstly, I will discuss the role of dimensionality on the electronphonon coupling and the energetics and size of polarons [3]. For this discussion I will illustrate recent methodological developments on the calculations of polar electronphonon interactions in two dimensions. Secondly, I will discuss our efforts to establish a manybody Green’s function framework for the ab initio polarons equations of Refs. [1,2]. I will show how polaron formation, phononinduced band gap renormalization, and phonon satellites in photoelectron spectroscopy can be rationalized within a unified conceptual framework. I will also discuss how the modern ab initio theory of polarons relates to earlier modelHamiltonian approaches to the polaron problem [4]. 
Tuesday, March 15, 2022 8:36AM  8:48AM 
F48.00002: Bandlike and Polaronic Charge Transport in Organic Crystals from FirstPrinciples Benjamin K Chang, NienEn Lee, JinJian Zhou, Marco Bernardi Predicting charge transport in organic molecular crystals (OMCs) is challenging due to their complex crystal structures and electronphonon (eph) interactions. In this talk, we will present two firstprinciples frameworks to accurately predict the charge carrier mobilities in OMCs. The first is the Boltzmann transport equation (BTE) with ab initio eph interactions, which describes the bandlike transport regime in OMCs [1]. We will show BTE calculations of hole mobilities in various molecular systems, and examine the effect of strain on charge transport. The second method is the cumulant plus GreenKubo (CK) [2,3], which addresses the regime where the eph interactions are of intermediate strength and the charge carriers form polarons. We will present our recent CK calculations of electron mobilities and electron spectral functions in OMCs. Both our BTE and CK approaches provide mobilities in very good agreement with experiments over a wide temperature range. These broadly applicable methods advance the understanding of charge transport in organic semiconductors. 
Tuesday, March 15, 2022 8:48AM  9:00AM 
F48.00003: Polarons in semilocal density functional theory: localization, manybody selfinteraction, and formation energy Stefano Falletta, Alfredo Pasquarello We develop a semilocal functional for overcoming the selfinteraction of electron and hole polarons by enforcing the piecewise linearity upon electron occupation. We obtain localized polarons with structural and electronic properties in agreement with references from a hybrid functional satisfying the same constraint. We then develop a scheme accounting for the effects of Fock exchange, further improving the formation energies. We demonstrate that the difference between the onebody and the manybody selfinteraction is related to screening effects. Case studies include the electron polaron in BiVO_{4}, the hole polaron in MgO, and the hole trapped at the Al impurity in αSiO_{2}. 
Tuesday, March 15, 2022 9:00AM  9:12AM 
F48.00004: Extending the Feynman polaron model for real materials Jarvist M Frost, Bradley A Martin Most new semiconductors proposed for energy storage and transformation are soft and polar leading to a large dielectric electronphonon coupling. This coupling drives the formation of polaron quasi particles, the electron dressed with phonon excitations. 
Tuesday, March 15, 2022 9:12AM  9:24AM 
F48.00005: Comparing the canonicaltransformation and energyfunctional approaches for ab initio calculations of selflocalized polarons yao luo, NienEn Lee, Marco Bernardi In materials with strong electronphonon (eph) interactions, charge carriers can distort the surrounding lattice and become trapped, forming selflocalized (small) polarons. Various theoretical treatments of small polarons have been proposed. We recently developed an ab initio approach based on canonical transformations that can efficiently compute the formation and energetics of small polarons with quantitative accuracy [1]. A different, energyfunctional approach has also been proposed in the literature [2]. In this talk, we compare these two methods using a unified formalism, which allows us to shed light on the physical effects included or neglected in these two approaches. We show that our canonical transformation formalism can properly include lattice vibrational effects while using a fixed polaron wave function. Conversely, we show that the energyfunctional approach neglects lattice vibrations and treats the electrons and phonons as decoupled; it attempts to describe the polaron wave function but misses the physics of polaron selflocalization and band narrowing. We will conclude our talk by presenting extensions of the canonical transformation approach to compute the polaron wave function as well as charge transport in the polaron hopping regime. 
Tuesday, March 15, 2022 9:24AM  9:36AM 
F48.00006: Sum Rules of the HolsteinHubbard Model and its Nonequilibrium Behavior Ryan D Nesselrodt, Khadijeh Najafi, James K Freericks, J. Alexander Jacoby With the proliferation of experimental techniques able to probe properties of complex materials in nonequilibrium with increasing accuracy and resolution, and interesting properties such as hidden phases continuing to garner interest, there is a clear need for accurate theoretical techniques to describe complex nonequilibrium processes. Few exact, manybody theoretical solutions exist in nonequilibrium, and approximations are very important. Sum rules, which relate integrals of the spectral function to expectation values of observables, may represent a selfconsistent way to check the accuracy of nonequilibrium calculations. And simple problems which can be solved exactly in nonequilibrium may provide insight on processes which may occur in more complicated nonequilibrium systems. We calculate the first three spectral moment sum rules for a general nonequilibrium HolsteinHubbard model. These moments can be verified exactly in the atomic limit, where an exact Green's function can be obtained. The behavior of this simpler Green's function's photoemission spectrum in nonequilibrium leads us to propose a measure, the first moment of the photoemission spectrum, which may be useful in tracking nonequilibrium changes in electronelectron or electronphonon couplings in systems with sufficiently separated energy bands. 
Tuesday, March 15, 2022 9:36AM  9:48AM Withdrawn 
F48.00007: Exact longrange dielectric screening and interatomic force constants in quasitwodimensional crystals Massimiliano Stengel, Miquel Royo The foundation of modern theory of lattice dynamics rests on the separation between shortrange and longrange interatomic force constants, where the latter are associated with macroscopic electric fields acting in a neighborhood of the Brillouin zone center. In threedimensional (3D) insulators, the famous dipoledipole formula was established long ago by Cochran and Cowley; the subsequent work of Pick, Cohen and Martin provided a formal derivation in the framework of firstprinciples theory. Very recently, we have incorporated higherorder interactions involving, e.g., dynamical quadrupoles, and demonstrated their role in the accurate interpolation of phonon band structures. In this talk, I shall retrace an analogous journey in the context of twodimensional (2D) crystals, by presenting a rigorous derivation of the longrange screening and interatomic forces in 2D. This enables a systematic generalization of the existing formulas (Sohier et al., Nano Lett. 2017, 17, 6, 3758– 3763) to an arbitrary multipolar order. In particular, I will discuss how to incorporate outofplane dipoles and dynamical quadrupoles in the longrange part of the dynamical matrix, and how to achieve an optimal representation of the dielectric function. Numerical tests on monolayer BN, SnS2 and BaTiO3 membranes demonstrate a drastic improvement in the description of the longrange electrostatic interactions, with comparable benefits to the quality of the interpolated phonon band structure. 
Tuesday, March 15, 2022 9:48AM  10:00AM 
F48.00008: Electronic Transport in twodimensional 2DMXenes for Energy Storage Nesrine Boussadoune, Olivier Nadeau, Gabriel Antonius One of the main scientific challenges in facing the world energy crisis is the efficient storage of renewable energy. To thisend, materials science relies increasingly on twodimensional (2D) materials for the development of highefficiency devices.MXenes, anewfamily of 2Dtransition metal carbides, nitridesand carbonitrides,with a general formula of Mn+1XnTx, have gainedgreat research attention in the energy storage devices, dueto their excellent electrical conductivity. In order to assist the design of supercapacitorselectrodes based on these materials, we investigate the structural, electronic and vibrational propertiesof pristine(Ti3C2) andfunctionalized MXenes(Ti3C2F2, Ti3C2(OH)2 and Ti2CF2)using firstprinciples calculations. Our goalisto understand how their electronic transport propertiesdepends on their morphology, chemical composition and surface termination,using density functional theory (DFT), density functional perturbation theory (DFPT)and the linearized Boltzmann transport equation (BTE). In this work, we will discuss the results and identifywhichone of theMXenes provide the higher electrical conductivity. This approach will pavea new way to design MXenesbased electrodesmaterials for energy storage applications 
Tuesday, March 15, 2022 10:00AM  10:12AM 
F48.00009: Copropagating edge states produced by the interaction between electrons and chiral phonons in twodimensional materials Luis E Foa Torres, Joaquín Medina Dueñas, Hernán L Calvo Unlike the chirality of electrons, the intrinsic chirality of phonons has only surfaced in recent years. Here we report on the effects of the interaction between electrons and chiral phonons in twodimensional materials by using a nonperturbative solution. We show that chiral phonons introduce inelastic Umklapp processes resulting in copropagating edge states which coexist with a continuum. Transport simulations further reveal the robustness of the edge states. Our results hint on the possibility of having a metal embedded with hybrid electronphonon states of matter. 
Tuesday, March 15, 2022 10:12AM  10:24AM 
F48.00010: Theory and Modeling of Optomechanics in Charge Density Wave Materials Anubhab Haldar, Cristian L Cortes, Stephen K Gray, Sahar Sharifzadeh, Pierre Darancet Novel materials with large optomechanical coupling coefficients are useful both for the exploration of fundamental lightmatter interactions, and for the application of their nonlinear response properties in nanoscale devices. Motivating and parameterizing simple phenomenological models of the dominant physics of such materials will provide an important connection between expensive firstprinciples calculations, and experimental observables. Using 1TTaS2 as a case study, we develop a general model for studying the coupling between phonons and change in polarizability. This model is successfully applied to the optomechanical response of the commensurate charge density wave (CDW) phase of 1TTaS2, where we can provide a simple physical explanation for the observation of the coherent 2.4 THz CDW amplitude mode that is observed in this system [1]. This model is generally applicable to materials where a change in symmetry is accompanied by a change in the polarizability of a system. 
Tuesday, March 15, 2022 10:24AM  10:36AM 
F48.00011: Ab initio prediction of modeselected surface electronphonon coupling strengths probed by Helium atom scattering (HAS) from the 3x1reconstructed Nb(001) surface oxide Michelle Kelley, Tomas A Arias, Alison McMillan, Caleb Thompson, Steven J Sibener Using densityfunctional theory (DFT), we demonstrate that our calculations are able to accurately capture the surface electronphonon physics at the (001) surface of niobium, the elemental superconductor with the highest critical temperature. The electronphonon interaction is the fundamental mechanism determining the properties of conventional superconductors, and theoretical predictions of surface properties of superconductors are critically important as external fields penetrating at surfaces limit the material’s overall performance. In this talk, we report surface phonon dispersions and surface electronphonon coupling strengths of the bare Nb(001) surface and the more complex Nb(001) surface with a longranged ordered, 3x1reconstructed oxide layer. We present our ab initio predictions of the 3x1O/NbO(001) system along with recent Helium atom scattering (HAS) which provide an experimental surface probe to directly measure modeselected electronphonon coupling strengths. The agreement between our DFT calculations and the HAS measurements on this nontrivial surface structure demonstrate the validity of our method and provide an exciting new application to predict surface electronphonon coupling strengths. 
Tuesday, March 15, 2022 10:36AM  10:48AM Withdrawn 
F48.00012: Midinfraredlightinduced structural symmetry breaking via nonlinear phononics Alaska Subedi There is much interest in accessing the brokensymmetry phases of crystals using light. However, an arbitrary light pulse, whose oscillating electric field integrates to zero by definition, imparts a zero total force to the electric dipole present in the material. Therefore, light pulses cannot in general be used to break the symmetries present in crystals. I present theoretical results that show that this limitation can be overcome if a strong quartic coupling of the type $Q_1^2Q_{\textrm{IR}}^2$ is present between a highfrequency infrared mode $Q_{\textrm{IR}}$ and a lowfrequency mode $Q_1$ with a negative coupling constant $g$. Realistic calculations show that such a coupling is present in oxide paraelectrics and can be used to induce ferroelectric phases using midinfrared pulses. 
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