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Thursday, March 17, 2022 3:00PM - 3:36PM Withdrawn |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 spin-orbit coupling in cross-coupling phenomena Invited Speaker: Silvia Picozzi During the last couple of decades, the spin-orbit 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 spin-orbit coupling (SOC), I will discuss two non-trivial aspects where this relativistic interaction gives rise to novel and exotic phenomena in multifunctional materials. First, I will focus on the ab-initio modelling of (non-magnetic) ferroelectric semiconductors, where SOC leads to a tight link between Rashba spin-splitting, spin-texture and electric polarization, with the appealing perspective of electric-field control of spin-degrees of freedom and long-sought integration of spintronics with ferroelectricity. Second, I will discuss first-principles 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 non-trivial spin configurations even in centrosymmetric systems. |
Thursday, March 17, 2022 3:36PM - 3:48PM |
W71.00002: Theory of Electron-Doped Ferroelectric Interfaces Bill Atkinson, Kelsey Chapman We introduce and describe a self-consistent model for a ferroelectric interface that is doped via the polar catastrophe mechanism, as would be expected in LaAlO3/Sr1-xCaxTiO3 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 S-shaped 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 low-polarization state with a negative susceptibility that is due to the formation of a head-to-head 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 Pb2CoTeO6 from first principles Md Kamal Hossain, Elizabeth A Nowadnick The B-site ordered double perovskite Pb2CoTeO6 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 non-polar structures P21/n (a+ b- b-)→I2/m (a0 b- b-)→R-3 (a- a- a-)→Fm-3m (a0 a0 a0). In order to investigate potential strategies to stabilize Pb2CoTeO6 in a polar structure, we use group-theoretic 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 Pb2CoTeO6 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 Pb2CoTeO6. |
Thursday, March 17, 2022 4:12PM - 4:24PM |
W71.00005: Chemically decomposed elastic properties from first principles: The elastic anomaly in PbTiO3 Guru S Khalsa, Ethan T Ritz, Hsin-Yu Ko, Robert A Distasio, Nicole A Benedek PbTiO3 is an important technological material due to its high-temperature ferroelectricity, piezoelectricity, and negative thermal expansion. Previous theoretical work has predicted an anomalously large elastic compliance in PbTiO3 that can be induced by negative pressure1, stress2,3, or strain3, 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 Ti-O bond along the polarization direction.1 |
Thursday, March 17, 2022 4:24PM - 4:36PM |
W71.00006: Symmetry-based approach to identify structural prototypes of ferroic phases Michele Kotiuga, Nicola Marzari, Giovanni Pizzi In previous work, we developed a systematic symmetry analysis using group-subgroup 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 lower-symmetry 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 higher-symmetry 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 5-atom conventional cell and is dependent on volume, the latter often dictated by the filler A-site cation.1 Furthermore, we investigate other lower-symmetry 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 ferroelectric-like 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 carrier-enhanced/induced ferroelectricity is still extremely rare. In this talk, we show that in a family of layered stannate oxides (hybrid-improper ferroelectric Ruddlesden-Popper 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 gating-induced `metallic-ferroelectricity' from the point of view of first-principles 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 strong-coupling limits of the electron-phonon interaction strength. We predict bipolaron formation in the strong-coupling regime, and binding at weak-coupling (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 strong-coupling 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 Exploration-Exploitation in N-Dimensional Functional Space of Material Properties using a Physics Driven Multi-Objective 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 trade-off between multiple functionalities is required to attain the desired material performance. In order to tackle these, we present Multi-objective Bayesian optimization (MOBO) workflow for the ferroelectric performance optimization based on the numerical solution of the Ginzburg-Landau 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 trade-offs between functionalities (Pareto frontier). Unlike exhaustive grid-based 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 physics-driven decision tree of target functions from the loop structures. Then, a physics-driven MOBO architecture is developed to build and explore Pareto-frontiers by optimizing user-chosen 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: Co-substituted BiFeO3: thermodynamic, electronic and ferroelectric properties from first principles Shivani Grover, Keith T Butler, Umesh V Waghmare, Ricardo Grau-Crespo The ferroelectric character of BiFeO3 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 BiCoxFe1‑xO 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 Co-substituted 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 Co-rich 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 Co-substituted BiFeO3 with relevant redox potentials, in the context of its applications in photocatalysis. |
Thursday, March 17, 2022 5:36PM - 5:48PM |
W71.00012: First-principles calculation of the bulk flexoelectric tensor Massimiliano Stengel, Miquel Royo The first-principles 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 long-wavelength acoustic phonons, within the framework of density-functional 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 by-product of the main linear-response calculation. |
Thursday, March 17, 2022 5:48PM - 6:00PM |
W71.00013: Active intrinsic symmetry-breaking in para-phase of cubic ABO3 perovskites and its effect on electronic properties Xingang Zhao, Oleksandr I Malyi, Alex Zunger The para-X phases (X=elastic, magnetic, and electric) of ABO3 perovskites represent spatial configurations of microscopic degree-of-freedoms (m-DOFs), i.e., local dipole/magnetic-moment/distortion. In their simple representations, these m-DOFs are assumed to be zero and are allowed to be non-zero only due to thermal agitation. Here, by minimizing internal energy in a cubically shaped supercell, we find that a distribution of intrinsic m-DOFs exists even before temperature sets in, being a polymorphous network and forming a precursor of para-phase. In contrast, many cubic compounds are never polymorphous, being stable without symmetry breaking as in BaZrO3. The formation of such distribution of m-DOFs leads to a change of electronic properties, such as mass-enhancement in paramagnetic SrVO3, piezoelectricity in paraelectric BaTiO3, and band gap opening in paraelastic BaBiO3. Interestingly, these effects are obtained in symmetry-broken DFT without explicit strong correlation. Our findings provide a theoretical interpretation of spontaneous symmetry-breaking in cubic para-phases. We also find cases where multiple m-DOFs coexist in a single system, leading to a significant change of electronic properties as in NaNbO3.
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