Bulletin of the American Physical Society
APS March Meeting 2019
Volume 64, Number 2
Monday–Friday, March 4–8, 2019; Boston, Massachusetts
Session A02: Dielectric & Ferroic Oxides -- Emergent Interfacial PhenomenaFocus
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Sponsoring Units: DMP DCOMP Chair: Lane Martin, University of Illinois at Urbana-Champaign Room: BCEC 107A |
Monday, March 4, 2019 8:00AM - 8:36AM |
A02.00001: Complex polarization textures and exotic properties in PbTiO3/SrTiO3 superlattices Invited Speaker: Javier Junquera When ultrathin ferroelectric layers of PbTiO3 are embedded in superlattices with a paraelectric material, such as SrTiO3, the interplay between elastic, electrostatic, and gradient energies produces complex patterns of the electrical polarization. In particular, nanometer scale of vortex-antivortex arrays have been recently detected [1], and exotic properties such as the emergence of a negative capacitance have been measured [2]. Performing predictive simulations in these systems is difficult due to the long spatial scales involved, the strong competition between a large number of phases and the sensitivity of the results to external perturbations like strain, periodicity, temperature or electric fields. In order to overcome these problems we employ a recently developed second-principles method [3] that can cope with all the degrees of freedom associated to a large number of atoms retaining high accuracy. Depending on the boundary conditions, our simulations predict the existence of several quasi-degenerate phases at low energies each displaying different properties including net polarization, negative capacitance [4], non-null topological constants [5] and chirality [5,6]. The later prediction supports the findings of optical activity in x-ray circular dichroism experiments [5,6]. Moreover, depending on the periodicity of the superlattice these chiral vortex phases coexist with ferroelectric phases and reversible phase transitions can be induced by external electric fields [7]. |
Monday, March 4, 2019 8:36AM - 8:48AM |
A02.00002: A theoretical design of inter-correlated in-plane and out-of-plane electric polarization in conventional perovskite ferroelectric thin films Wenguang Zhu, Tianping Gu Ferroelectric materials may have multiaxial electric polarization, in particular, in-plane and out-of-plane orientations for ferroelectric thin films, but the reversal of their electric polarization along different axes is normally independent. In this talk, I will present a theoretical design to make conventional perovskite ferroelectric thin films have inter-correlated in-plane and out-of-plane electric polarization, based on first-principles calculations. This work may lead to new device paradigms and applications based on conventional perovskite ferroelectric thin films. |
Monday, March 4, 2019 8:48AM - 9:00AM |
A02.00003: Charge Density imaging of a ferroelectric-insulator interface with sub-Å resolution Christopher Addiego, Wenpei Gao, Hui Wang, Xingxu Yan, YUSHENG HOU, Dianxiang Ji, Colin Heikes, Yi Zhang, Linze Li, Huaixun Huyan, Thomas F Blum, Toshihiro Aoki, Yuefeng Nie, Darrell G. Schlom, Ruqian Wu, Xiaoqing Pan In complex oxide heterostructures, charge redistribution determines the characteristics of the material and can have significant influence on the behavior of the material. For example, the 2-dimensional electron gas at an LaAlO3-SrTiO3 interface is linked with superconductivity and ferromagnetism at the interface [1]. Although first principles calculations can provide highly detailed charge density maps that illustrate these phenomena, experimental methods often cannot resolve the same features at interfaces or nanostructures with high spatial resolution. Here we demonstrate the imaging of electron charge at interfaces in heterogeneous perovskite structures at atomic resolution using aberration corrected scanning transmission electron microscopy. The charge density mapping is determined using the 2D diffraction pattern acquired with a high-speed pixelated detector [2]. At a BiFeO3-SrTiO3 interface, we found evidence of charge separation caused by the penetration of the electric field from the polarized BiFeO3 into the insulating SrTiO3. |
Monday, March 4, 2019 9:00AM - 9:12AM |
A02.00004: Probing ferroelectric switching of BaTiO3 thin films integrated on Silicon Marc Reynaud, Johanna Nordlander, Felix Eltes, Gabriele De Luca, Jacob Nürnberg, Stefan Abel, Jean Fompeyrine, Manfred Fiebig, Alexander Demkov, Morgan Trassin The integration of ferroelectric materials on Si plays an important role in the design of new photonic devices, such as optical switches and modulators. Ferroelectric materials exhibit nonlinear optical properties and in particular their refractive index can be tuned by the application of an E-field via the Pockels effect. Ferroelectric barium titanate (BTO) thin films can be epitaxially grown on silicon, using molecular beam epitaxy (MBE). Controlling the polarization of thin these films in absence of metallic buffer remains non-trivial. Orienting the polar axis beyond the limitation of epitaxy using voltage induced ferroelastic switching events to generate out-of-plane (c-domains) to in-plane polarization (a-domains) rotation would open up new pathways for fabricating photonic devices. In this study, we use transmission optical second harmonic generation (SHG) to study the ferroelastic switching dynamics in our BTO films grown on Si for varying thicknesses. The orientation of the BTO films polar axis and the a/c-domain ratio before and after the application of an external in plane E-field are mapped. |
Monday, March 4, 2019 9:12AM - 9:48AM |
A02.00005: Making and manipulating ferroelectric vortices, a TEM perspective of nanoscale flux closure in dielectrically confined PbTiO3 films Invited Speaker: Christopher Nelson A prominent disparity between the two ferroic siblings of ferromagnetism and ferroelectricity is the exciting complex topologies appearing in the spin distributions of former while the electric dipole textures of the latter flag behind. By engineering the scale and field energy minimization pressures driving flux closure formation we realize in SrTiO3 encapsulated ferroelectric PbTiO3 thin films the formation of nanoscale ferroelectric vortices. With (S)TEM we characterize the structure of these ~5nm vortices down to atomic scales and study the transition from long-range vortex arrays to in-plane a-domains with decreasing superlattice period, including a mixed structure regime and extrinsic formation of vortices in thicknesses below the vortex-stability limit. Using in-situ applied electric bias we observe the dynamic field-response including the creation, deformation, motion, and erasure of these ferroelectric vortices. |
Monday, March 4, 2019 9:48AM - 10:00AM |
A02.00006: Ionic Gating Driven Polarization Control in Ultra-Thin and Leaky Ferroelectrics Yogesh Sharma, Nina Balke, Ho Nyung Lee, Thomas Ward Ionic liquid (IL) gating allows large electric fields to be achieved at the interface— providing an ability to control, manipulate, and elevate unique phenomena that can arise in the interfaced solid materials. Here, Ionic gating is used to induce reversible polarization switching in ultrathin and highly defective ferroelectric films. Long range electrostatic charge control is induced by modifying the electric double layer at an IL–PbZr0.2Ti0.8O3 interface which drives electrostatic and electrochemical control of polarization orientation in the ferroelectric layer. The localized nature of the ionic gating mechanism forbids the leakage current which has historically limited the switching of ultra-thin and/or electrically leaky ferroelectric films in solid metal-gated capacitor devices. This is demonstrated on ultrathin films and in intentionally grown massively defective films with > 30% coverage of direct conducting channels running from surface to ground. We will close by discussing how the transient switching and the ability to manipulate static analog phase transitions might impact future technologies. |
Monday, March 4, 2019 10:00AM - 10:12AM |
A02.00007: Possible Flexoelectric Origin of the Lifshitz Transition in LaAlO3/SrTiO3 Interfaces Amany Raslan, Bill Atkinson Multiple experiments have observed a sharp transition in the band structure of LaAlO3/SrTiO3 (001) interfaces as a function of applied gate voltage. This Lifshitz transition, between a single occupied band at low electron density and multiple occupied bands at high density, is remarkable for its abruptness. We propose a mechanism by which such a transition might happen. We show via numerical modeling that the simultaneous coupling of the dielectric polarization to the interfacial strain (``electrostrictive coupling'') and strain gradient (``flexoelectric coupling'') generates a thin polarized layer whose direction reverses at a critical density. The Lifshitz transition occurs concomitantly with the polarization reversal and is first-order at T=0. A secondary Lifshitz transition, in which electrons spread out into semiclassical tails, occurs at a higher density. |
Monday, March 4, 2019 10:12AM - 10:24AM |
A02.00008: WITHDRAWN ABSTRACT
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Monday, March 4, 2019 10:24AM - 10:36AM |
A02.00009: First Principle Study of the Si-EuO Interface Wente Li, Alexander Demkov As scaling in the conventional semiconductor industry continues, including the electronic spin degree offers new ways of information processing. The choice of materials in semiconductor spintronics needs to provide efficient spin injection and detection along with the long coherent length and relaxation time in the semiconductor. Silicon offers a long spin relaxation time. And EuO is a promising ferromagnetic semiconductor, at least at low temperature. Due to its high spin polarization and thermodynamic stability on Si, epitaxial EuO may be a good candidate for application of spintronics. We use first principle calculations to study the atomic and electronic structure of the Si-EuO interface. We construct Si-EuO interface models and analyze the band alignment at the interface, our results suggest that Si-EuO heterostructure is a feasible option for spin injector in Si-based spintronic devices. |
Monday, March 4, 2019 10:36AM - 10:48AM |
A02.00010: Electrical transport properties of two-dimensional materials on ferroelectrics toward nonvolatile memory devices Nahee Park, Haeyong Kang, Dongseok Suh When ferroelectric material is employed as a gate dielectric for the field effect transistor (FET) of a two-dimensional (2D) material such as graphene, MoS2, and MoTe2, it is possible to induce a giant amount of carriers in the channel by polarization field of the ferroelectric and also to show a nonvolatile memory operation. In many cases, however, the electrical coupling between 2D material and ferroelectric-oxide had shown abnormal behavior like anti-hysteresis different from 2D material/ferroelectric-polymer cases showing normal hysteresis. In our work, we also observed systematically those phenomena related to the interface by combining ferroelectric oxide material, PMN-PT (i.e. (1-x)Pb(Mg1/3Nb2/3)O3-PbTiO3) single-crystal with several 2D materials. Through the electrical transport measurement, it is found out that the ferroelectric polarization and trapped charges strongly interacts each other, which is reflected in the conductance of 2D channel. To develop the 2D electronic system in ferroelectric memory device, we should study those properties in detail. |
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