Bulletin of the American Physical Society
APS March Meeting 2017
Volume 62, Number 4
Monday–Friday, March 13–17, 2017; New Orleans, Louisiana
Session F19: DCOMP Metropolis Award Session: Electric Polarization and Novel Routes to FerroelectricityInvited Prize/Award
|
Hide Abstracts |
Sponsoring Units: DCOMP DCMP Chair: David Vanderbilt, Rutgers University Room: 278-279 |
Tuesday, March 14, 2017 11:15AM - 11:51AM |
F19.00001: The theory of polarization: From its origins to the modern day Invited Speaker: Raffaele Resta Textbooks define macroscopic polarization {\bf P} as the dipole of a bounded sample, divided by its volume, in the large sample limit. When instead we address unbounded samples within periodic boundary conditions (PBCs) the above definition cannot be adopted. The breakthrough came 25 years ago, when the focus was shifted from {\bf P} itself to adiabatic changes in {\bf P}, and it was soon realized that such changes take the form of a Berry phase of the electronic wavefunction. Even {\bf P} itself can be defined, but it is {\it not} a vector: it is a lattice. Such exotic feature has outstanding physical consequences. For instance for an insulating centrosymmetric polymer P is a $Z_2$ invariant: either P=e/2 mod e, or P=0 mod e: the $Z_2$ class depends on the bulk, while the ``mod'' value depends on actual termination of the bounded sample. Besides {\bf P}, other quantum-mechanical observables are based on the ``bare'' position ${\bf r}$, which is not a legitimate operator within PBCs: foremost among them is orbital magnetization {\bf M}. Here I express such observables in terms of a ``projected'' position operator $\tilde{\bf r}$, which is legitimate for both bounded and unbounded samples, and yields very compact expressions for the relevant PBCs formulae. Besides {\bf P} and {\bf M}, I will also express in terms of $\tilde{\bf r}$ the anomalous Hall conductivity (for insulators and metals), and the Marzari-Vanderbilt gauge-invariant quadratic spread. [Preview Abstract] |
Tuesday, March 14, 2017 11:51AM - 12:27PM |
F19.00002: Multiscale Simulations of Dynamics of Ferroelectric Domains Invited Speaker: Shi Liu Ferroelectrics with switchable polarization have many important technological applications, which heavily rely on the interactions between the polarization and external perturbations. Understanding the dynamical response of ferroelectric materials is crucial for the discovery and development of new design principles and engineering strategies for optimized and breakthrough applications of ferroelectrics. We developed a multiscale computational approach that combines methods at different length and time scales to elucidate the connection between local structures, domain dynamics, and macroscopic finite-temperature properties of ferroelectrics. We started from first-principles calculations of ferroelectrics to build a model interatomic potential, enabling large-scale molecular dynamics (MD) simulations. The atomistic insights of nucleation and growth at the domain wall obtained from MD were then incorporated into a continuum model within the framework of Landau-Ginzburg-Devonshire theory. This progressive theoretical framework allows for the first time an efficient and accurate estimation of macroscopic properties such as the coercive field for a broad range of ferroelectrics from first-principles. \footnote{S. Liu, I. Grinberg, and A. M. Rappe, Nature, 534, 360-363 (2016)}This multiscale approach has also been applied to explore the effect of dipolar defects on ferroelectric switching and to understand the origin of giant electro-strain coupling. [Preview Abstract] |
Tuesday, March 14, 2017 12:27PM - 1:03PM |
F19.00003: Theory of hyperferroelectrics Invited Speaker: Kevin F. Garrity Typical proper ferroelectrics are unable to polarize normal to a surface or interface if the resulting depolarization field is unscreened. However, there is no fundamental principle that enforces this behavior. This talk will introduce and review recent progress in the field of hyperferroelectrics, a new class of proper ferroelectrics that polarize even when the depolarization field is unscreened ($D\!=\!0$ electrostatic boundary conditions). Hyperferroelectrics display a variety of properties that differ from typical ferroelectrics, including unstable longitudinal optic (LO) phonon modes, a qualitatively different electric equation of state, and unusual dielectric behavior. These properties may enable useful functionalities like single layer ferroelectric films as well as head-to-head and tail-to-tail domain walls. In this talk, I will introduce the theory of hyperferroelectrics as seen in $ABC$ semiconducting ferroelectrics and ferroelectric superlattices. Then, I will consider recently proposed materials realizations of hyperferroelectrics, including in SrNb$_6$O$_{16}$, which was identified in a high-throughput search for new ferroelectrics. I will also briefly discuss the behavior of hyperferroelectrics with strong spin-orbit coupling, which enables a persistent and reversible coupling between the polarization and electronic properties like the Rashba effect and even topological states. [Preview Abstract] |
Tuesday, March 14, 2017 1:03PM - 1:39PM |
F19.00004: Polarization activated by Jahn-Teller distortions in perovskites and vice versa Invited Speaker: Philippe Ghosez Although prototypical ferroelectrics such as BaTiO$_3$ and PbTiO$_3$ belong to the family of ABO$_3$ perovskite compounds, relatively few perovskite oxides are in fact ferroelectrics. Some years ago, a new type of improper ferroelectricity -- nowadays referred to as ``hybrid improper ferroelectricity’’ -- has been discovered in layered perovskites, highlighting an alternative mechanism to achieve ferroelectricity in this family of compounds. In hybrid improper ferroelectrics, the polarization is activated by the appearance of a combination of two independent non-polar atomic distortions. So far, most efforts have focused on systems in which these non-polar distortions are anti-ferrodistortive rotation motions of the oxygen cages. In this talk, I will show that, in some systems, polarization can alternatively be activated by non-polar Jahn-Teller distortions or, vice versa, Jahn-Teller distortions can be activated by the polarization. This will be exemplified both in layered and bulk perovskites. In these systems, the intimate coupling between polarization and Jahn-Teller distortions is not only of academic interest but reveals also a promising pathway to achieve electric control of the electronic properties. [Preview Abstract] |
Tuesday, March 14, 2017 1:39PM - 2:15PM |
F19.00005: Control of octahedral rotations for the design of largely enhanced ferroelectricity and related functionalities in perovskites Invited Speaker: Xifan Wu Ferroelectric polarization in perovskite materials is closely associated with the pattern of its oxygen octahedral rotations, which are common structural distortions in perovskites. The oxygen rotation pattern in BiFeO$_3$ with R3C symmetry promotes large electric polarization. On the contrary, oxygen rotation pattern in CaTiO$_3$ of Pbnm symmetry strongly suppresses the ferroelectricity. For many CaTiO$_3$-like perovskites, the BiFeO$_3$-like structure is a metastable phase. Our Landau phenomenological theory reveals that the stability of either a CaTiO$_3$-like or a BiFeO$_3$-like structure in perovskite is sensitively dependent on the structural distortions, which could be effectively adjusted by material engineering approaches and external stimulus. Here, we report the stabilization of the highly-polar BiFeO$_3$-like phase in nonpolar orthorhombic perovskites based on interface engineering, epitaxial strain, applied electric fields etc. Our results suggest that a large number of perovskites with the CaTiO$_3$ structure type, which include many magnetic representatives, are now good candidates as novel highly-polar multiferroic materials. [Preview Abstract] |
Follow Us |
Engage
Become an APS Member |
My APS
Renew Membership |
Information for |
About APSThe American Physical Society (APS) is a non-profit membership organization working to advance the knowledge of physics. |
© 2024 American Physical Society
| All rights reserved | Terms of Use
| Contact Us
Headquarters
1 Physics Ellipse, College Park, MD 20740-3844
(301) 209-3200
Editorial Office
100 Motor Pkwy, Suite 110, Hauppauge, NY 11788
(631) 591-4000
Office of Public Affairs
529 14th St NW, Suite 1050, Washington, D.C. 20045-2001
(202) 662-8700