Bulletin of the American Physical Society
APS March Meeting 2023
Volume 68, Number 3
Las Vegas, Nevada (March 510)
Virtual (March 2022); Time Zone: Pacific Time
Session M41: Theoretical and Computational Modeling of Ferroelectrics and MultiferroicsFocus

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Sponsoring Units: DMP Chair: Yang Zhang, University of Tennessee Room: Room 319 
Wednesday, March 8, 2023 8:00AM  8:36AM 
M41.00001: Magnetoelectric multipoles and spin textures in realspace and reciprocal space Invited Speaker: Sayantika Bhowal In condensed matter systems, the multipoles provide a quantitative measure of the complex angular distribution of the charge and magnetization densities in a brokensymmetry phase of a solid. Magnetoelectric multipoles, that break both spaceinversion I and timereversal T symmetries, quantify the antisymmetric magnetization density of a solid. In my talk, I will discuss a general theory to classify magnetic skyrmions and related spin textures in terms of their magnetoelectric multipoles [1]. Since magnetic skyrmions are now established in insulating materials, where the magnetoelectric multipoles govern the linear magnetoelectric response, our classification provides a recipe for manipulating the magnetic properties of skyrmions using applied electric fields. Taking the examples of skyrmions, antiskyrmions, and bimerons of different helicities, we show that the nonzero components of the magnetoelectric multipole and magnetoelectric response tensors are uniquely determined by the topology, helicity, and geometry of the spin texture. We have proposed straightforward linear magnetoelectric response measurements as an alternative to Lorentz microscopy for characterizing insulating skyrmionic textures. Similarly, to the description of realspace spin textures by realspace magnetoelectric multipoles, momentumspace spin textures can also be described by kspace magnetoelectric multipoles [2]. These kspace magnetoelectric multipoles are reciprocal to the realspace charge dipoles associated with the broken inversion symmetry. Using the prototypical ferroelectric PbTiO_{3} as an example material, I will discuss the tuning of the kspace magnetoelectric multipoles and their possible detection using designed magnetic Compton scattering techniques. 
Wednesday, March 8, 2023 8:36AM  8:48AM 
M41.00002: Theory of domain structure in electrondoped ferroelectric thin films Bill Atkinson To reduce the energy cost of strong depolarizing fields, insulating ferroelectric often films break up into nanoscale ``Kittel'' domains of opposite polarization that are separated by uncharged 180^{? }domain walls. Here, I report on recent selfconsistent solutions of coupled LandauGinzburgDevonshire and Schrödinger equations for an electrondoped ferroelectric thin film. The model is based on LaAlO3/SrTiO3 interfaces in which the SrTiO3 substrate is made ferroelectric by cation substitution or strain. Electron doping destabilizes the Kittel domains. As the twodimensional electron density increases, there is a smooth crossover to a zigzag domain wall configuration. The domain wall is positively charged, but is compensated by the electron gas, which attaches itself to the domain wall and screens depolarizing fields. The domain wall approaches a flat headtohead configuration in the limit of perfect screening. The polarization profile may be manipulated by an external bias voltage and the electron gas may be switched between surfaces of the ferroelectric film. 
Wednesday, March 8, 2023 8:48AM  9:00AM 
M41.00003: Modeling Local Distortions in Zn_{1x}Mg_{x}O Ferroelectrics Steven M Baksa, Ismaila Dabo Nonvon Neumann computing architectures offer opportunities to maximize the energy efficiency and floatingpointcomputation performance of microprocessors, beyond the von Neumann computing model in which the datastorage and dataprocessing functions of the computer are physically separated. One example of such architectures is threedimensional ferroelectric microelectronics (3DFeMs) that take advantage of thirddimensional interconnects, enabling lowpower computation. The integration of ferroelectric memory capabilities into fieldeffect transistors requires the development of ferroelectric materials that would be scalable and compatible with current microelectronic technologies. In this work, we study the mechanisms of polarization switching in recently proposed Zn_{1−x}Mg_{x}O (ZMO) ferroelectric materials. To understand cation ordering in ZMO at finite temperature, we validated and applied largescale Monte Carlo simulations in the canonical ensemble using Metropolis and WangLandau samplings. Finitetemperature Monte Carlo simulations strongly suggest that shortrange cation ordering critically influence the stability and ferroelectric response of ZMO compounds. Analyzing local distortions associated with temperaturedependent cation ordering may ultimately provide insight into the mechanisms facilitating polarization switching in ZMO. 
Wednesday, March 8, 2023 9:00AM  9:12AM 
M41.00004: Spinpolarized Flexoelectricity John Cavin, James M Rondinelli Flexoelectricity describes the coupling between electric polarization and a strain gradient. Firstprinciples methods for calculating flexoelectric tensor components have been previously developed that involve calculating electronic and lattice contributions using various chargemoment and force tensors. In magnetic materials, these charge moments can be spinpolarized – that is, the densities of spin up and down electrons can respond differently to atomic displacement. Based on this principle, we developed a method for calculating spinpolarized flexoelectric tensor components. We apply our method to a ferromagnetic oxide finding a sizeable spinpolarization of the flexoelectric tensor. Furthermore, we calculate its three independent flexoelectric tensor components and use these to predict an effective spinpolarized beambending flexoelectric constant along the (100) direction. The potential applications to spintronics through a metaloxide interface is discussed. 
Wednesday, March 8, 2023 9:12AM  9:24AM 
M41.00005: Understanding Dynamics of Heterogeneous Ferroelectric Oxides at the Nanoscale using Graph Neural Networks on Reactive ForceField Simulations Abhijeet S Dhakane, Tian Xie, Bobby G Sumpter, Dundar Yilmaz, Adri C Van Duin, Panchapakesan Ganesh Ferroelectrics are a technologically important class of materials for next generation microelectronics platforms, such as ferroelectric memristors, which show spontaneous longrange ordering of electric polarization. Recent advances have even shown formation of novel nanoscale chiral polar structures, such as polar skyrmions in heterogeneous oxides, that open new possibilities for storing and manipulating information at the nanoscale. While formation of longrange polar order as well as polar skyrmions is understood to be a delicate balance between coupling between microscopic degrees of freedom, there is a critical need to understand dynamics of polarization switching in such heterogeneous materials under high fields. In this talk, we will present insights into the dynamics of polarization switching in defective BaTiO_{3}, obtained from combining largescale atomistic reactive simulations with dynamical graph neural network approaches. Specifically, we will focus on how polarstructure and dynamics changes around pointdefects, and how this interaction influences domainwall dynamics. 
Wednesday, March 8, 2023 9:24AM  9:36AM 
M41.00006: Dynamic Atomic Offcentering and Its Selective Coupling with Phonons in KTa_{(1x)}Nb_{x}O_{3} Xing He, Olivier Delaire, Douglas L Abernathy, Garrett E Granroth, Feng Ye, Lynn A Boatner The mechanism of ferroelectric phase transitions (e.g. displacive or orderdisorder) in simple compounds like BaTiO_{3 }and KNbO_{3 }has remained debated for decades. Finally solving this question requires simultaneously resolving atomic dynamics, local crystal distortions and complex correlated disorder. To address this challenge, we map the energy and momentum resolved dynamic structure factor S(Q, E) with neutron scattering and we perform DFTaccuracy machinelearning MD (MLMD) simulations, to rationalize the spatial and temporal correlations of atomic disorder and the coupling with phonons. Here, we focus on correlated atomic offcentering in KTaO_{3} and KTa_{(1−x)}Nb_{x}O_{3 }(KTN) and find an intermediate picture between displacive and orderdisorder scenarios. Our experiments show twodimensional diffuse sheets from correlated local disorder in KTN, contrasting with displacive KTaO_{3}. Our firstprinciples and MLMD simulations reveal that correlated 1D chains of offcentered Bsite atoms in KTN are energetically favorable, and show how the correlated disorder selectively couples with the ferroelectric instability as well as transverse acoustic modes. These results provide insights into these model systems and offer general guidance for related systems whose atomistic behavior remain debated. 
Wednesday, March 8, 2023 9:36AM  9:48AM 
M41.00007: Theory of ElectroOptic Response in Tetragonal BaTiO_{3} Inhwan Kim, Alexander A Demkov The linear electrooptic (EO), or Pockels effect offers a promising path to fabrication of ultralow power ultracompact electrooptic modulators in silicon photonics bridging the optical technology with conventional silicon. Barium titanate, BaTiO_{3 }(BTO), has emerged as a promising electrooptic material that can be integrated with silicon photonics. In this talk, we report the first principles calculations of the EO or Pockels tensor in tetragonal BTO. Due to the lattice anharmonicity, predicting the Pockels response using functional theory (DFT) has been a challenge. However, our results indicate that the problem may be deeper. We show that the conventional P4mm structure of BTO is most likely a dynamic average of lower symmetry structures in agreement with recent experiments [1]. Using this argument as a starting point, we calculate both the ionic and piezo contributions of the EO tensor in good agreement with available experimental values. 
Wednesday, March 8, 2023 9:48AM  10:00AM 
M41.00008: FerroX : A GPUaccelerated, 3D PhaseField Simulation Framework for Modeling Ferroelectric Devices Prabhat Kumar, Andrew J Nonaka, Revathi Jambunathan, Girish Pahwa, Sayeef Salahuddin, Zhi Yao Fundamental understanding and design of ferroelectric/multiferroic materials and devices for logicinmemory and transistor enhancement is essential to enable low switching energies and thereby revolutionary power reductions in computing. Efficient modeling and simulations can provide indepth insights into the underlying physics, as well as pave the road to facilitate researchers with reliable design tools for new microelectronic devices. In this talk, we will present a performanceportable, 3D phasefield simulation framework, FerroX, for modeling and design of ferroelectricbased microelectronic devices. FerroX is opensource (https://github.com/AMReXMicroelectronics/FerroX) and demonstrates a significant (15x) speedup on GPU architectures compared to the CPU counterparts. We will demonstrate the application of the code with simulations of multidomain negative capacitance effects in MetalFerroelectricInsulatorMetal (MFIM) and MetalFerroelectricInsulatorSemiconductorMetal (MFISM) devices. Additionally, we will report the latest upgrades, including the addition of strain in total free energy of ferroelectrics and the development of a micromagnetic module for modeling multiferroics. 
Wednesday, March 8, 2023 10:00AM  10:12AM 
M41.00009: Manipulation of spin orientation in irondoped ferroelectric oxides from first principles Elizabeth A Nowadnick, Katherine Inzani, Nabaraj Pokhrel, Nima Leclerc, Sriram Ramkumar, Zachary Clemens, Sinead M Griffin

Wednesday, March 8, 2023 10:12AM  10:24AM 
M41.00010: Ferroelectric switching pathways, domain structure, and domain wall vortex in SrBi_{2}(Ta,Nb)_{2}O_{9} Nabaraj Pokhrel, Elizabeth A Nowadnick Aurivilliusphase oxides SrBi_{2}B_{2}O_{9} (B=Ta, Nb) are room temperature ferroelectrics which are well known for their fatigue resistance, low coercive fields, and potential application in ferroelectric randomaccess memory. Previous work has shown that the trilinear coupling between the electrical polarization and two octahedral rotation distortions of different symmetries plays a key role in the structural phase transition sequence and stabilization of the ferroelectric phase in SrBi_{2}Ta_{2}O_{9}. However, the implications of the trilinear coupling on the ferroelectric switching mechanism in these materials remain to be understood. In this work, we use the group theoretic analysis and density functional theory calculations to enumerate and explore the energetics of ferroelectric switching paths in SrBi_{2}B_{2}O_{9 }and identify several lowenergy one and twostep ferroelectric switching pathways. Moreover, we show how the relative energy barriers of these switching paths can provide the insight into the domain structure of these oxides. In particular, our findings indicate that threefold domain wall vortices are energetically favorable in SrBi_{2}B_{2}O_{9} which corroborates experimental reports of the domain structure in SrBi_{2}Ta_{2}O_{9}. This work advances our fundamental understanding of the technologically important family Aurivillius oxides. 
Wednesday, March 8, 2023 10:24AM  10:36AM 
M41.00011: Exploring Electrically Controlled Magnons for PostMoore Microelectronics with Exascale Modeling Zhi (Jackie) Yao, Prabhat Kumar, Andy Nonaka, Revathi Jambunathan, Xianzhe Chen, Xiaoxi Huang, Ramamoorthy Ramesh The postMoore's law era has seen unprecedented growth of electronic microdevices harnessing novel physical couplings beyond conventional singlephase materials. To gain an indepth understanding of the interaction between the physical mechanisms, we are exploring the validation, design and optimization of magnetoelectric spinorbit logics. Using the GPUaccelerated software package we have developed (https://github.com/AMReXMicroelectronics), we are studying the manipulation of chiralspin transport with ferroelectric polarization, which allows control of magnons by external electric fields. With the capability to explore full physical interactions, this new approach provides a pathway to understand and develop new fully integrated electronic systems beyond the capability of traditional semiconductor technologies. 
Wednesday, March 8, 2023 10:36AM  10:48AM 
M41.00012: Firstprinciples theory of phonon magnetic moment Xiaowei Zhang, Chong Wang, Yafei Ren, Ting Cao, Di Xiao Chiral phonons have recently been shown to possess finite magnetic moment that consists of both nuclei and electron contributions. Classical (using Born effective charge) and quantum theories for the electron’s contribution have both been developed. However, the two theories carry essential differences in handling the geometric effects, and quantitative comparisons between the two theories are missing in realistic materials. Here, we developed a firstprinciples scheme to calculate phonon magnetic moment from quantum theory. We found observable magnetic moments of chiral phonon modes in a gated twodimensional material. In contrast, the magnetic moments vanish according to classical theory. This contrast highlights the central role of geometric effects in phonon magnetic moments. In addition, the magnetic moments have significant electricfield tunability and mode selectivity. Our numerical methods and predictions open a new route to finding dynamical multiferroicity in realist material systems. 
Wednesday, March 8, 2023 10:48AM  11:00AM 
M41.00013: Local symmetry breaking in different phases of BaTiO_{3} Xingang Zhao, Oleksandr I Malyi, Sandra H Skjærvø, Simon L Billinge, Alex Zunger Macroscopically, the different phases of BaTiO_{3} have been generally understood by considering an averaged structure with the ordered local dipole or without the local dipole. However, microscopically, the local dipole configurations (LDC) in different phases remain poorly understood except for the ground state BaTiO_{3}. Experimental local probes, e.g., pair distribution function (PDF), and frequencydependent structure factor S(q,w), as well as density functional theory (DFT) calculations[1] reveal that the LDC in their averaged crystal structures, especially in cubic, does not describe well the system. Here, using DFT including in finite T Molecular Dynamics and minimizing the energy (E=UTS) in supercells, we find the existence of LDC in all the phases of BaTiO_{3} before & after temperature sets in. Except for ground state BaTiO_{3}, the calculated and measured LDC in different phases differentiates from the ordered LDC or no LDC from their averaged structures. Further direct comparisons between the calculated PDF and S(q,w) based on the DFT minimized structures and the experimental measured PDF and S(q, w) confirm that local symmetry breaking due to LDC in different phases of BaTiO_{3}. Our work bridges the theoretical simulation to the experimentally local measurement. 
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