Bulletin of the American Physical Society
APS March Meeting 2020
Volume 65, Number 1
Monday–Friday, March 2–6, 2020; Denver, Colorado
Session R64: Chiral and Polar Structures in Thin Film OxidesFocus
|
Hide Abstracts |
Sponsoring Units: DMP DCOMP Chair: Kaveh Ahadi, NC State University Room: Mile High Ballroom 4E |
Thursday, March 5, 2020 8:00AM - 8:36AM |
R64.00001: Electric-field control of emergent chirality in PbTiO3/SrTiO3 superlattices Invited Speaker: Margaret McCarter Novel chiral phases in ferroelectric materials—the polar analogs of magnetic vortices and skyrmions—can be stabilized in superlattices of PbTiO3 and SrTiO3. These chiral structures emerge in low-dimensional ferroelectrics, where the competition among gradient, electrostatic, and elastic energies favors non-uniform polarization configurations. Such phases can lead to new functional properties such as negative capacitance as well as unique interactions with polarized light. The characterization of these new phases and their three-dimensional chiral structure remains a challenge due to limitations of conventional electron microscopy and X-ray diffraction techniques. |
Thursday, March 5, 2020 8:36AM - 8:48AM |
R64.00002: Atomic Structure Underlying Vortex Polarization Domains in Hexagonal RMnO3 Sizhan Liu, Matthew Newville, Antonio Lanzirotti, Sang-Wook Cheong, Trevor Tyson Hexagonal phase RMnO3 systems exhibit polarization domains with complex vortex patterns with density depending on the cooling rate from the high-temperature paraelectric phase. Detailed polarization mapping is being compared with spatially dependent structural and spectroscopic studies to related variations in the domain patters with local atomic and electronic structure. Structural measurements reveal variations on the lenghtscale of the changes in polarization. |
Thursday, March 5, 2020 8:48AM - 9:00AM |
R64.00003: Negative capacitance in polar skyrmions Sujit Das, Zijian Hong, Vladimir A Stoica, Mauro A. P. Gonçalves, Eric Parsonnet, Sahar Saremi, Margaret McCarter, Armando Reynoso, Derek Meyers, Vishal Ravi, Hua Zhou, Zhan Zhang, Haidan Wen, Fernando Gómez-Ortiz, Pablo Garcia-Fernandez, Jeffrey Bokor, Jorge Iniguez, John William Freeland, Javier Junquera, Long Q. Chen, Sayeef Salauddin, Lane Wyatt Martin, Ramamoorthy Ramesh Topological solitons such as magnetic skyrmions have drawn enormous attention as stable quasi-particle-like objects. The recent discovery of polar vortices and skyrmions in ferroelectric oxide superlattices, exhibiting exotic physical phenomena, has opened up new vistas to explore topology, emergent phenomena, and approaches for manipulating such features with electric fields [1,2]. Here, using macroscopic dielectric measurements, phase-field simulations, and second-principles calculations, we demonstrate that polar skyrmions in (PbTiO3)n/(SrTiO3)nsuperlattices are distinguished by a sheath of negative permittivity at the periphery of each skyrmion which enables a strong enhancement of the effective dielectric permittivity as compared to the individual SrTiO3and PbTiO3 layers. Electric-field-dependent X-ray scattering measurements, phase-field simulations, and second-principles calculations are used to determine the relative fraction of skyrmions and quantify the local dielectric susceptibilities. A large, electric-field tunable negative permittivity provides a fundamental framework to enable novel low-power electronics. |
Thursday, March 5, 2020 9:00AM - 9:12AM |
R64.00004: Polar Domains in Strained SrTiO3 Films Salva Salmani-Rezaie, Kaveh Ahadi, Susanne Stemmer We report on the microscopic mechanisms of how the incipient ferroelectric SrTiO3 transforms into a ferroelectric by epitaxial strain. These films have recently been shown to have enhanced superconducting transition temperatures when doped, pointing to a relationship between superconductivity and ferroelectricity order parameters. Here, using high-angle annual dark-field scanning transmission electron microscopy, we detect local polar regions at room-temperature in compressively strained and unstrained SrTiO3 films, respectively. Our image analysis uses the average deviation of the Ti column from the cubic position as the polar order parameter. We find that unstrained SrTiO3 stays paraelectric while compressively strained films show short-range cooperative displacements within nano polar regions at room temperature. The observation of polar regions may explain optical second harmonic generation (SHG) studies, showing a residual SHG signal at room temperature in strained SrTiO3. Oxygen annealing suppresses the formation of polar regions, highlighting the importance of free carriers for the stability of the polar regions. |
Thursday, March 5, 2020 9:12AM - 9:24AM |
R64.00005: Strain-Induced Ferroelectricity in Freestanding SrTiO3 Membranes Ruijuan Xu, Jiawei Huang, Ed Barnard, Seung Sae Hong, Ed Wong, Varun Harbola, Prastuti Singh, Bai Yang Wang, Shi Liu, Harold Hwang SrTiO3 is known to exhibit quantum paraelectricity in which quantum fluctuations suppress ferroelectric ordering at low temperature. Despite the intrinsic paraelectric nature of SrTiO3, epitaxial strain applied via the lattice mismatch in thin-film heterostructures can significantly enhance the ferroelectric transition temperature Tc. Here we utilize freestanding crystalline membranes to extend the lattice control of ferroelectric ordering in SrTiO3. By dissolving a water-soluble buffer layer, we release SrTiO3 films from substrates, and transfer the resulting freestanding membranes onto flexible substrates that can be dynamically stretched into various strain states. Using second harmonic generation microscopy, we probe the ferroelectric phase transition as a function of strain wherein we observe Tc is significantly enhanced by strain. Upon applying 1.5% uniaxial strain, we observe robust room-temperature ferroelectricity with the notable feature of 180° ferroelectric domains using piezoresponse force microscopy. First-principle calculations and molecular dynamics simulations further reveal the structural nature at each given strain state and the order-disorder character of phase transition in strained SrTiO3 membranes. |
Thursday, March 5, 2020 9:24AM - 9:36AM |
R64.00006: Manipulation of superdomains in Pb(Zr0.2Ti0.8)O3 epitaxial films grown on SrTiO3 (110) substrates Yi-Chun Chen, Heng-Jui Liu, Yu-Chen Liu, Meng-Xun Xie, Yu-Huai Li, Sheng-Zhu Ho, Yi-Chia Chou, Ying-Hao Chu, Jan-Chi Yang Various interesting physical properties arising from manipulating strain energy terms in epitaxial films have attracted great attention. For tetragonal Pb(Zr0.2Ti0.8)O3 (PZT) films, the large piezoelectric response mainly originates from the switching of 90-degree c/a domains due to the strain-relief-induced reorientation. In this study, we found a superdomain structure existing the epitaxial PZT films when grown on the (110)-oriented SrTiO3 (STO). The in-plane strain from STO breaks the uniaxial symmetry of the tetragonal PZT film, and with suitable adjusting the strain energy, superdomains can be formed in long-range areas. We used X-ray diffraction, transmission electron microscopy, and piezoresponse force microscopy (PFM) to investigate the distortion of crystal and domain structures. The PFM images show periodic nanodomains with size about 50-80 nm in the superdomain region and indicate the coexistence of at least two distortions of the crystal. The superdomains can be effectively induced or erased by external fields. Based on systematical investigations, the mechanism to create superdomains by electric fields is concluded relating to the surface energy. This study provides basic understanding and control of this unique superdomain structure. |
Thursday, March 5, 2020 9:36AM - 9:48AM |
R64.00007: Low-temperature synthesis of BaTiO3 thin film by molecular beam epitaxy Yeongjae Shin, Juan Jiang, Yichen Jia, Frederick J Walker, Charles H Ahn The perovskite oxide BaTiO3 is a lead-free material with high performance ferroelectric/piezoelectric properties. Integrating BaTiO3 with existing semiconductor technology requires the synthesis of high-quality BaTiO3 in the thin-film form at low temperatures to decrease the thermal budget during device fabrication. We describe our synthesis of BaTiO3 thin films by molecular beam epitaxy at various temperatures and find that coherently strained BaTiO3 can be grown at a temperature as low as 280 °C. The growth mechanism and strain state of these films are characterized as a function of temperature using x-ray diffraction and in-situ reflection high-energy electron diffraction. Our results pave the way toward large-scale integration of BaTiO3 with semiconductor technology. |
Thursday, March 5, 2020 9:48AM - 10:00AM |
R64.00008: Monoclinic Phase and Interphase Boundaries in Perovskite Ferroelectrics Tyler Liebsch, Vladimir Sobolev The temperature intervals of phase coexistence, including the recent experimentally observed monoclinic phase, in ferroelectric BaTiO3 have been investigated using the Landau-Ginzburg-Devonshire phenomenological approach. Comparison of the thermodynamic potential for all phases in BaTiO3 showed that the monoclinic phase is metastable near the tetragonal-orthorhombic phase transition, in the absence of an electric field. The structure and width of the interphase boundaries separating domains of coexisting phases near the phase transitions have been analyzed. The temperature dependence of polarization distributions, width, and energy density of the interphase boundary separating the tetragonal and monoclinic phases as well as the orthorhombic and monoclinic phases were found. The obtained results for interphase boundaries were compared to previous experimental and theoretical results for the domain walls existing within the above-mentioned phases. |
Thursday, March 5, 2020 10:00AM - 10:12AM |
R64.00009: Surface Proximity Effect, Imprint Memory of Ferroelectric Twins, and Tweed in the Paraelectric Phase of BaTiO3 Nicholas Barrett, Claire Mathieu, Christophe Lubin, Pascale Gemeiner, Brahim Dkhil, Ekhard Salje For post-CMOS electronics applications using ferroic materials, the surface can play a crucial role. Non-invasive techniques are required to study the chemistry and electronic structure underlying their unique electrical properties. The sensitivity of photoemission (PEEM) electron microscopy to local surface potential, chemistry and electronic structure makes it a useful tool for probing the ferroic surfaces. |
Thursday, March 5, 2020 10:12AM - 10:24AM |
R64.00010: Coherent Acoustic Phonons and Ultrafast Carrier Dynamics in BaTiO3-BiFeO3Films and Nanorods Rathsara R Herath Mudiyanselage, Brenden A Magill, Giti Khodaparast, Christopher J Stanton, Jade Holleman, Stephen A McGill, Min-Gyu Kang, Han-Byul Kang, Shashank Priya BiFeO3 has become a popular multiferroic material as an alternative to PZT since it is lead free. The addition of about 25% BaTiO3 in solid solution has been shown to substantially improve the coupling between electric, magnetic, optical, and structural orders parameters and offers the possibility of developing high speed multifunctional devices. We performed two-color (400 nm pump, 800 nm probe) time resolved transient reflectivity measurements of (1-x) BaTiO3 -(x) BiFeO3, with x = 0.725 and BaTiO3-BiFeO3 nanorods. Our results show ultrafast carrier dynamics in BaTiO3-BiFeO3, which we interpret as diffusion of the photoexcited carriers away from the surface with an ambipolar diffusion constant that is below 1-2 cm2/s.The differential reflectivity also showed evidence of coherent acoustic phonons (CP) in both the films and nanorod samples at lower temperatures (100 K).. The ability to generate strain via ultrafast optics can offer the intriguing possibility of dynamically manipulating and controlling electric and magnetic fields. |
Thursday, March 5, 2020 10:24AM - 10:36AM |
R64.00011: Understanding the ferroelectric switching in freestanding BiFeO3 films Qiwu Shi, Yen-Lin Huang, Hongrui Zhang, Xiaoxi Huang, Sujit Das, Ramamoorthy Ramesh The goal to achieve the low-voltage switching in BiFeO3 could be significant for reducing the energy consumption for the electric field control of magnetism, and promoting the prospect of ultra-low power ferroelectric memories. Although several strategies have been proposed, such as size scaling, strain engineering or achieving high-quality of crystals, the value of switching voltage has been still limited. In this work, we design the freestanding BiFeO3 films for elucidating the ferroelectricity without the “clamping effect” from substrate. Due to the release of the imposed strain from substrate, the lattice distortion and a reduced c/a value are observed. And the ferroelectric domain pattern of BiFeO3 shows a highly-order to disorder transition after freestanding. This inhomogeneous domain structure might be induced by the release of the clamping effect from the substrate and could be one of the reasons for the reduced switching voltage in the freestanding BiFeO3. It indicates that the freestanding methodology may pave a new pathway toward the next-generation low-power ferroelectric memory. |
Thursday, March 5, 2020 10:36AM - 10:48AM |
R64.00012: Manipulation of spin and the effective spin-orbit coupling in complex oxides Weichuan Huang, Sujit Das, Ruchira Chatterjee, Katherine Inzani, Evan Sheridan, Sinéad Griffin, Valentin V. Laguta, Yen-Lin Huang, Hongrui Zhang, Ramamoorthy Ramesh Electric field manipulation of spins and control of spin-orbital coupling have stimulated an intense interest due to their promise for new functionalities and power efficient device concepts. We are particularly interested in the manipulation of spin state (high spin to low spin) as well as their directionality, for example in a d5 state Fe3+ ion. Using Fe-doped PbTiO3 (Fe-PTO) as a model system, we present a systematic study of the thickness, temperature and electric field-dependent spin manipulations and spin-orbit coupling (SOC) effect in dilute magnetic ferroelectrics. Using laser MBE, we synthesized a series of Fe-PTO thin films with thickness range from 15 nm to 200 nm on various substrates in order to access systematically strained states in the Fe-PTO layer. Electron spin resonance from the Fe-site demonstrates a strong g-factor anisotropy from the normal to in-plane direction of the films. Moreover, we observed that the g-factor anisotropy systematically changes under tensile strain. These results demonstrate the manipulation of spins as well as effective SOC by subtle aspects of lattice strain/electric field. |
Thursday, March 5, 2020 10:48AM - 11:00AM |
R64.00013: Octahedral rotations in Ruddlesden-Popper layered perovskites under pressure from first principles Sriram Poyyapakkam Ramkumar, Elizabeth Nowadnick Octahedral rotations are ubiquitous in perovskite oxides and couple closely to their electronic and magnetic properties. Applying pressure to bulk perovskites tunes the octahedral rotation amplitudes, and in some cases changes the octahedral rotation pattern. While the pressure response of octahedral rotations in ABO3 perovskites has been well studied, the impact of pressure on layered perovskites such as the n=2 Ruddlesden-Popper (RP) phase A3B2O7 is much less explored. Here, we use density functional theory calculations to investigate the pressure response of several A3B2O7 layered pervoskites. We find that these RPs have a distinct pressure response compared to ABO3 materials. In particular, while the pressure response of ABO3 perovskites often can be classified according to the charge state of the A- and B-site cations, we find that each of the A32+B24+O7 RPs that we study exhibits a different response to pressure. Using a Landau expansion, we show how the interplay between different energetic contributions in RPs leads to this diverse set of responses to pressure. Our results offer insight into how to tune the structure and hence properties such as ferroelectricity in layered perovskites. |
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