Bulletin of the American Physical Society
APS March Meeting 2022
Volume 67, Number 3
Monday–Friday, March 14–18, 2022; Chicago
Session W71: Theoretical and Computational Modeling of Ferroelectrics and MultiferroicsFocus Recordings Available

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Sponsoring Units: DMP Chair: Zahra Hooshmand Gharehbagh, University of Texas El Paso Room: Hyatt Regency Hotel Jackson Park C 
Thursday, March 17, 2022 3:00PM  3:36PM Withdrawn 
W71.00001: From Rashba Ferroelectrics to exotic spin textures: the role of spinorbit coupling in crosscoupling phenomena Invited Speaker: Silvia Picozzi During the last couple of decades, the spinorbit interaction has played an increasingly crucial role in condensed matter physics, thanks to its relevance as a rich microscopic mechanism from the fundamental point of view and as a driving force for innovative spintronic applications on the technological side. After a general overview on spinorbit coupling (SOC), I will discuss two nontrivial aspects where this relativistic interaction gives rise to novel and exotic phenomena in multifunctional materials. First, I will focus on the abinitio modelling of (nonmagnetic) ferroelectric semiconductors, where SOC leads to a tight link between Rashba spinsplitting, spintexture and electric polarization, with the appealing perspective of electricfield control of spindegrees of freedom and longsought integration of spintronics with ferroelectricity. Second, I will discuss firstprinciples results for 2D magnets, where SOC can play a relevant role in the emergence of multiferroicity as well as of a large anisotropic exchange coupling. The latter is also put forward as a novel and alternative mechanism that can possibly give rise to topologically nontrivial spin configurations even in centrosymmetric systems. 
Thursday, March 17, 2022 3:36PM  3:48PM 
W71.00002: Theory of ElectronDoped Ferroelectric Interfaces Bill Atkinson, Kelsey Chapman We introduce and describe a selfconsistent model for a ferroelectric interface that is doped via the polar catastrophe mechanism, as would be expected in LaAlO_{3}/Sr_{1x}Ca_{x}TiO_{3} interfaces. We find that the resultant metallic state is characterized by the intertwining of lattice polarization and electronic degrees of freedom; the electron gas binds to polarization gradients to form a compensated state with net vanishing charge density. In this way, depolarizing fields are screened while external fields remain at least partly unscreened. Thus, in contrast to naive expectations that the free electron gas screens external fields, we find Sshaped hysteretic polarization curves as a function of bias voltage. We argue that switchable metallic films may be optimized by tuning the electron density to be slightly less than the lattice polarization; at higher electron densities, a fraction of the electron gas spills over to the interface and interferes with the switchability of the electronic state. We find, in addition, a lowpolarization state with a negative susceptibility that is due to the formation of a headtohead domain wall. This domain formation is enabled by the screening of depolarizing fields by the electron gas. 
Thursday, March 17, 2022 3:48PM  4:00PM 
W71.00003: Microscopic polarization and magnetization fields: Including spin effects Alistair H Duff, John E Sipe We extend a microscopic theory of polarization and magnetization to include the spin degree of freedom of the electrons. The microscopic polarization and magnetization fields are introduced throughout an extended system using a set of orthogonal orbitals associated with each site. As well free charge and current density fields are introduced associated with charge movement from site to site. The sites act as natural expansion points when evaluating the perturbative response of the multipole moments to applied electromagnetic fields that can be at arbitrary frequency and vary over the unit cell. Associated with the dipole moments are the respective macroscopic polarization and magnetization fields, from which we can extract the various material response tensors. For example, in the limit of uniform fields, we recover the magnetoelectric polarizability tensor, which contains the accepted expression for the orbital magnetoelectric polarizability as well as a straightforward spin dependent contribution. This general framework can also be extended to treat the spin current response in materials. 
Thursday, March 17, 2022 4:00PM  4:12PM 
W71.00004: Structural instabilities of double perovskite Pb_{2}CoTeO_{6} from first principles Md Kamal Hossain, Elizabeth A Nowadnick The Bsite ordered double perovskite Pb_{2}CoTeO_{6} is an attractive multiferroic candidate due to the presence of the lone pair cation Pb and the magnetic cation Co. However, experimental work so far has not reported a polar phase, instead detecting a structural phase transition sequence with increasing temperature between the nonpolar structures P2_{1}/n (a^{+} b^{} b^{})→I2/m (a^{0} b^{} b^{})→R3 (a^{} a^{} a^{})→Fm3m (a^{0} a^{0} a^{0}). In order to investigate potential strategies to stabilize Pb_{2}CoTeO_{6 }in a polar structure, we use grouptheoretic analysis to enumerate possible space groups involving octahedral rotations, polar cation displacements, and combinations of these distortions. We then utilize density functional theory calculations to explore the energetics and crystal structure of Pb_{2}CoTeO_{6 }when confined to each of these symmetries. We also explore how epitaxial strain modifies the relative energies and structural distortion amplitudes of the various structural phases of Pb_{2}CoTeO_{6}. 
Thursday, March 17, 2022 4:12PM  4:24PM 
W71.00005: Chemically decomposed elastic properties from first principles: The elastic anomaly in PbTiO_{3} Guru S Khalsa, Ethan T Ritz, HsinYu Ko, Robert A Distasio, Nicole A Benedek PbTiO_{3} is an important technological material due to its hightemperature ferroelectricity, piezoelectricity, and negative thermal expansion. Previous theoretical work has predicted an anomalously large elastic compliance in PbTiO_{3} that can be induced by negative pressure^{1}, stress^{2,3}, or strain^{3}, and could potentially be exploited in applications requiring large tailored piezoelectric and elastic responses. The microscopic mechanism of this anomalous behavior remains unknown but has been hypothesized to involve breaking of the TiO bond along the polarization direction.^{1} 
Thursday, March 17, 2022 4:24PM  4:36PM 
W71.00006: Symmetrybased approach to identify structural prototypes of ferroic phases Michele Kotiuga, Nicola Marzari, Giovanni Pizzi In previous work, we developed a systematic symmetry analysis using groupsubgroup relations to construct representative structural models for ferroic phases in the form of supercells that satisfy a desired point symmetry but are built from the minical combination of lowersymmetry primitive cells [M. Kotiuga et al., arXiv:2107.04628]. This allowed us to identify structural prototypes (i.e., supercells that are lower in energy, per formula unit, than the highersymmetry primitive cell and with real, positive phonon dispersions) of paraelectric barium titanate characterized by〈111〉local titanium displacements while preserving cubic point symmetry. Here, we extend this study to several other cubic perovskites and show that the metastability of these prototypes is related to the phonon instabilities of the 5atom conventional cell and is dependent on volume, the latter often dictated by the filler Asite cation.^{1} Furthermore, we investigate other lowersymmetry phases of perovskites in order to identify the structural prototypes of both ferroelectric and antiferroelectric phases of these materials.^{2} This approach is general and can be used in any crystalline system to find candidate templates and efficiently search for prototypes. 
Thursday, March 17, 2022 4:36PM  4:48PM 
W71.00007: Can free charge carriers induce structural polarization? Shutong Li, Turan Birol Free charge carriers are often detrimental to ferroelectricity due to the screening of long range coulomb interactions. Thus the design of a metal that undergoes a ferroelectriclike phase transition (from a centrosymmetric to a structurally phase) is challenging. Although recent studies has shown the mutual existence of ferroelectricity and metallicity in several systems, the carrierenhanced/induced ferroelectricity is still extremely rare. In this talk, we show that in a family of layered stannate oxides (hybridimproper ferroelectric RuddlesdenPopper phases) the polarization can actually be strengthened and even induced through the introduction of free carriers via electrostatic gating. We also investigate the microscopic mechanism and design criteria for this kind of gatinginduced `metallicferroelectricity' from the point of view of firstprinciples calculations. The possibility of expanding this phenomenon to other compounds are also discussed. 
Thursday, March 17, 2022 4:48PM  5:00PM 
W71.00008: Analysis of Fröhlich bipolarons Lisa Lin Following a resurgence of interest in dilute superconductivity in polar semiconductors such as strontium titanate (STO) and potassium tantalate (KTO), we perform a variational calculation to probe the existence of Fröhlich bipolarons in this class of materials. Our solution is capable of interpolating between the weak and strongcoupling limits of the electronphonon interaction strength. We predict bipolaron formation in the strongcoupling regime, and binding at weakcoupling (close to ferroelectricity) only when the electron size is extrinsically restricted. We find measurable binding at STO parameters that may be relevant to experiment, and are not aware of any materials in the strongcoupling regime. 
Thursday, March 17, 2022 5:00PM  5:12PM 
W71.00009: A Real Space Approach to Uniqueness in Polarization SHOHAM SEN, Kaushik Dayal A fundamental issue in the atomic and quantum scale modeling of dielectric materials is the question of 
Thursday, March 17, 2022 5:12PM  5:24PM 
W71.00010: An Approach to Rapid ExplorationExploitation in NDimensional Functional Space of Material Properties using a Physics Driven MultiObjective Bayesian optimization Arpan Biswas, Anna N. Morozovska, Maxim Ziatdinov, Eugene A. Eliseev, Sergei V. Kalinin For any specific application, optimal parameters choice is critical in finding the desired material properties. However, the complexity arises with high dimensional parameter space, and where the functional map between material parameter and response is unknown or expensive. The complexity furthermore increases, even where generative physical model of material behavior is known and reliable, when a tradeoff between multiple functionalities is required to attain the desired material performance. In order to tackle these, we present Multiobjective Bayesian optimization (MOBO) workflow for the ferroelectric performance optimization based on the numerical solution of the GinzburgLandau equation with electrochemical or semiconducting boundary conditions. In MOBO, each unknown/expensive functional forms are represented with computationally cheap posterior Gaussian process models fitted from prior evaluations, and then select future evaluations through exploration/exploitation from maximizing an acquisition function, ultimately to identify the set of optimal solutions at different tradeoffs between functionalities (Pareto frontier). Unlike exhaustive gridbased search, this approach uses adaptive sampling technique and attempt for minimal expensive evaluations to reach towards the goal. In this work, with the parameters for a prototype bulk antiferroelectric (PbZrO3), we first develop a physicsdriven decision tree of target functions from the loop structures. Then, a physicsdriven MOBO architecture is developed to build and explore Paretofrontiers by optimizing userchosen multiple target functions jointly. This approach allows for rapid initial materials and device parameter selection for a given application and can be further expanded towards the active experiment setting to reduce time and effort. 
Thursday, March 17, 2022 5:24PM  5:36PM 
W71.00011: Cosubstituted BiFeO_{3}: thermodynamic, electronic and ferroelectric properties from first principles Shivani Grover, Keith T Butler, Umesh V Waghmare, Ricardo GrauCrespo The ferroelectric character of BiFeO_{3} might enhance carrier separation in photocatalytic applications, but its efficiency is limited by a wide electronic bandgap. We have investigated the thermodynamic, electronic, and ferroelectric properties of BiCo_{x}Fe_{1‑x}O solid solutions, 0<x<0.13, using density functional theory. The bandgap can be reduced from 2.9 eV to 2.1 eV upon Co substitution, while simultaneously enhancing ferroelectric behavior: a large spontaneous polarization is predicted for the Cosubstituted system, due to an anomalously large Born effective charge of Co compared to Fe cations. We discuss the interaction between Co impurities, which is strongly attractive and would drive the aggregation of Co at temperatures of interest, as evidenced by Monte Carlo simulations. Phase separation into a Corich phase is therefore predicted to be thermodynamically preferred, but a homogeneous solid solution with this composition can probably exist in metastable form, protected by slow cation diffusion kinetics. Finally, we discuss the band alignment of pure and Cosubstituted BiFeO_{3} with relevant redox potentials, in the context of its applications in photocatalysis. 
Thursday, March 17, 2022 5:36PM  5:48PM 
W71.00012: Firstprinciples calculation of the bulk flexoelectric tensor Massimiliano Stengel, Miquel Royo The firstprinciples theory of flexoelectricity has made impressive progress since the early pioneering works back in 2010. [R. Resta, PRL 105, 127601; J. Hong et al., JPCM 22, 112201] The main difficulty in dealing with the flexoelectric effect, i.e., the breakdown of translational symmetry, has been overcome since then by reformulating the problem in terms of longwavelength acoustic phonons, within the framework of densityfunctional perturbation theory (DFPT). As of early 2020, a complete implementation of the bulk flexoelectric tensor is fully integrated in the latest release of the ABINIT package, which is now publicly available. Additional surface contributions have also been understood and can be accessed as a byproduct of the main linearresponse calculation. 
Thursday, March 17, 2022 5:48PM  6:00PM 
W71.00013: Active intrinsic symmetrybreaking in paraphase of cubic ABO_{3} perovskites and its effect on electronic properties Xingang Zhao, Oleksandr I Malyi, Alex Zunger The paraX phases (X=elastic, magnetic, and electric) of ABO_{3} perovskites represent spatial configurations of microscopic degreeoffreedoms (mDOFs), i.e., local dipole/magneticmoment/distortion. In their simple representations, these mDOFs are assumed to be zero_{ }and are allowed to be nonzero only due to thermal agitation. Here, by minimizing internal energy in a cubically shaped supercell, we find that a distribution of intrinsic mDOFs exists even before temperature sets in, being a polymorphous network and forming a precursor of paraphase. In contrast, many cubic compounds_{ }are never polymorphous, being stable without symmetry breaking as in BaZrO_{3}. The formation of such distribution of mDOFs leads to a change of electronic properties, such as massenhancement in paramagnetic SrVO_{3}, piezoelectricity in paraelectric BaTiO_{3}, and band gap opening in paraelastic BaBiO_{3}. Interestingly, these effects are obtained in symmetrybroken DFT without explicit strong correlation. Our findings provide a theoretical interpretation of spontaneous symmetrybreaking in cubic paraphases. We also find cases where multiple mDOFs coexist in a single system, leading to a significant change of electronic properties as in NaNbO_{3}.

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