Bulletin of the American Physical Society
APS March Meeting 2020
Volume 65, Number 1
Monday–Friday, March 2–6, 2020; Denver, Colorado
Session P64: Carriers in Ferroelectrics and Multiferroic Quantum CriticalityFocus
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Sponsoring Units: DMP DCOMP Chair: Katherine Inzani, Lawrence Berkeley National Laboratory Room: Mile High Ballroom 4E |
Wednesday, March 4, 2020 2:30PM - 2:42PM |
P64.00001: Origin of Metal–Insulator Transition in n-doped ABO3 Perovskite Metals Guoxiang Hu, Chandler Bennett, Qiyang Lu, Olle Heinonen, Paul Kent, Ho Nyung Lee, Jaron Krogel, Panchapakesan Ganesh A subclass of ABOx perovskites undergoes metal-to-insulator transitions (MITs) when n-doped either via oxygen vacancies concomitant with ordering, chemical substitution or strain. For example, the oxygen-rich perovskite SrCoO3 is a ferromagnetic metal, while the oxygen-deficient brownmillerite SrCoO2.5 is an anti-ferromagnetic insulator. The precise mechanism driving the MIT, and its relation to the electronic-structure of the metallic phase, remains unknown. Here we hypothesize that metallic ABO3 that are more susceptible to a MIT via n-doping are self-hole doped negative charge transfer metals; n-doping fills these pre-existing holes and gives rise to an insulating state. Magnetism is a secondary effect that may or may not assist in the gap opening. Moreover, this tendency to remain self-hole doped determines a universal electronic response to modulations in stoichiometry/composition/pressure. In this work, we use ab-initio density functional theory (DFT), DFT+U, DFT+hybrid as well as many-body quantum Monte Carlo (QMC) calculations to shed light on the hypothesis, with comparison to experiments where possible. |
Wednesday, March 4, 2020 2:42PM - 2:54PM |
P64.00002: Pressure-induced metal-insulator transition in degenerately doped ferroelectrics Chengliang Xia, Yue Chen, Hanghui Chen
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Wednesday, March 4, 2020 2:54PM - 3:06PM |
P64.00003: Can free charge carriers enhance polarization? Shutong Li, Turan Birol Ferroelectricity and metallicity has long been thought to be mutually exclusive because of the screening of the long range coulomb force. After the observation of ferroelectric-like transitions in metals recently, there has been a surge of interest in the study of `ferroelectric metals’ and the stabilizing forces of structural polarization therein. Nevertheless, addition of carriers to semiconducting or insulating ferroelectrics is still usually thought to be detrimental to ferroelectricity. In this talk we show, by using first principles calculations, that ferroelectric polarization can actually be strengthened by introduction of free carriers in a series of oxide ferroelectrics. We consider introduction of carriers through electrostatic gating, which can alter the carrier concentration without changing the level of disorder. |
Wednesday, March 4, 2020 3:06PM - 3:18PM |
P64.00004: Dielectric Conduction in the Post-breakdown Region Predicted Using a Charge Transport Model Yueming Xu, Joel L Plawsky, Toh-Ming Lu A Charge Transport Model was developed originally in our group to predict time-dependent dielectric breakdown (TDDB) in the back end of line (BEOL) interconnects. Both ramped voltage stress tests (RVS) and constant bias stress tests (CVS) data could be simulated with a same set of fitting parameters by the model. |
Wednesday, March 4, 2020 3:18PM - 3:30PM |
P64.00005: A high-throughput search of antiferroelectric perovskites. Hugo Aramberri, Jorge Iniguez Despite the perovskite family of compounds showing a plethora of polymorphs with rich ferroic behaviors, the quest for an antiferroelectric perovskite oxide with a simple displacive behavior remains fruitless (but for maybe PbZrO3). By means of first principles calculations, we carry out a high-throughput study of non-magnetic perovskites (ABO3), comparing their leading instabilities in their vibrational spectra and their known experimental polymorphs. Most remarkably, this search has allowed us to identify a family of perovskite-derivative compounds that display a rich variety of polar and non-polar polymorphs and seem promising candidates for antiferroelectric behavior. |
Wednesday, March 4, 2020 3:30PM - 3:42PM |
P64.00006: Frustrated Dipole Order Induces Noncollinear Proper Ferrielectricity in Two Dimensions Ling-Fang Lin, Yang Zhang, Adriana Moreo, Elbio Dagotto, Shuai Dong Achieving novel physical properties in two-dimensional (2D) materials should enable numerous functionalities in nanoscale devices. In recent years, interest in high-performance 2D ferroelectric materials has also grown rapidly across multiple scientific and engineering disciplines. Here, dioxydihalides MO2X2 materials (where M= Mo and W; X= Cl and Br) are studied based on density functional theory calculations. For dioxydihalides MO2X2 monolayers, we predict that they should display noncollinear ferrielectricity, induced by competing ferroelectric and antiferroelectric softmodes [1]. More importantly, this intrinsic noncollinearity of dipoles generates unique physical properties, such as Z2xZ2 topological domains, atomic-scale dipole vortices/anti-vortices, and negative piezoelectricity. Our investigations should open the door to a new branch of 2D materials in the pursuit of intrinsically strong noncollinear ferrielectricity. |
Wednesday, March 4, 2020 3:42PM - 3:54PM |
P64.00007: A room-temperature ferroelectric semimetal Pankaj Sharma Ferroelectricity has often been associated with and observed in materials that are insulating or semiconducting rather than metallic because conduction electrons in metals screen out the static internal fields arising from a long-range dipolar order. In the 1960s, Anderson and Blount proposed materials with these seemingly incompatible characteristics, i.e., metals with a polar axis termed ferroelectric metals. Since then, ferroelectric metals were merely a theoretical construct until recent experimental observations suggesting otherwise. Despite the progress, electrically switchable intrinsic electric polarization, together with the direct observation of ferroelectric domains, has not yet been realized in a bulk crystalline metal, although incomplete screening by mobile conduction charges should, in principle, be possible. |
Wednesday, March 4, 2020 3:54PM - 4:06PM |
P64.00008: The Role of Oxide Surface Structure and Polarity in Flexoelectricity Christopher Mizzi, Laurence D. Marks Interest in flexoelectricity has grown significantly over the past decade owing to its universality and importance at the nanoscale. Unlike many other oxide properties, a material’s macroscopic flexoelectric response is predicted to be highly surface sensitive. This surface sensitivity has been demonstrated with first principles calculations on (100) SrTiO3 bulk terminations [PRB 90, 201112(R) (2014)]. However, experimentally observed oxide surfaces often possess structural and chemical differences from the corresponding bulk material, the effects of which remain unclear in the context of flexoelectricity. Using density functional calculations, we compare the flexoelectric response of a number of low-energy (100) SrTiO3 reconstructions to assess the impact of surface stoichiometry and periodicity on flexoelectricity. Additionally, we address the role of polar surfaces with calculations on (100) and (111) MgO surfaces. Our calculations on experimentally observed oxide surface structures corroborate previous work highlighting the importance of surfaces in flexoelectricity and have important implications for flexoelectric measurements and thin film growth. |
Wednesday, March 4, 2020 4:06PM - 4:18PM |
P64.00009: Uniqueness of the Polarization in Crystals and Nanostructures Shoham Sen, Yang Wang, Pradeep Sharma, Kaushik Dayal Ionic crystals such as solid electrolytes and complex oxides are central to modern technologies for energy storage, sensing, actuation, and other functional applications. An important fundamental issue in the atomic and quantum scale modeling of these materials is the question of defining the macroscopic polarization. In a periodic crystal, the usual definition of the polarization as the first moment of the charge density in a unit cell is found to depend qualitatively and quantitatively on the choice of the unit cell. |
Wednesday, March 4, 2020 4:18PM - 4:54PM |
P64.00010: Multiferroic Quantum Criticality Invited Speaker: Awadhesh Narayan Phase transitions are ubiquitous in nature -- water turning to steam is an everyday example. A special kind of phase transition can occur at zero temperature by changing a non-thermal control parameter. Such a quantum phase transition is the driver for exotic quantum critical physics that extends to elevated temperatures [1]. In this talk, I will begin by introducing quantum phase transitions in magnets, which have been widely explored [2]. I will next discuss, the very recently established, ferroelectric quantum critical behavior [3]. Finally, I will present the concept of multiferroic quantum criticality -- in which both magnetic and ferroelectric quantum criticality occur in the same system -- that we have recently proposed [4]. I will describe the associated experimental signatures and material systems to realize it, and highlight possible future directions. |
Wednesday, March 4, 2020 4:54PM - 5:06PM |
P64.00011: Dynamical hybrid improper ferroelectricity in incipient ferroelectric SrTiO3 Mingqiang Gu, James Rondinelli SrTiO3 (STO) has been intensively studied, in part, because of its ‘incipient’ ferroelectricity. A small perturbation, such as strain, stress, chemical variation, or surface truncation, can induce a paraelectric to ferroelectric phase transition. Recent optical pump-probe experiments found that even THz light excitations can trigger the transition in STO. The underlying mechanism for the light-mediated ferroelectricity remains controversial; explaining it is crucial for both ultrafast manipulation and control. Here, we explain this process as a form of dynamical hybrid improper ferroelectricity. The inversion symmetry is lifted by the trilinear coupling between a polar mode, a zone-center antiferrodistortive mode, and a zone-boundary in-phase rotation mode activated under THz pumping. With density functional theory calculations, we compute the free energy profiles of the coupled modes. With the fitted coupling coefficients, we estimate the time evolution of the inversion symmetry lifting and compare our model with the experimental results. Our understanding extends the scope of improper ferroelectricity, and may open a new route to manipulate inversion symmetry of other materials in the time domain. |
Wednesday, March 4, 2020 5:06PM - 5:18PM |
P64.00012: Multiferroic Switching Dynamics in BiFeO3 Eric Parsonnet, Yen-Lin Huang, Chia-Ching Lin, Tanay Gosavi, Alexander Qualls, Ian Young, Lane Wyatt Martin, Jeffrey Bokor, Ramamoorthy Ramesh With room temperature coupling between magnetic and electric degrees of freedom, BiFeO3 (BFO) has attracted much attention as a leading candidate for magnetoelectric applications. There has been extensive work studying quasi-static magnetoelectric coupling in BFO, but the magnetoelectric coupling dynamics, their fundamental speed limits and intrinsic mechanisms of switching have yet to be explored. We are studying time-domain switching dynamics of the ferroelectric state as the first step in understanding magnetoelectric dynamics. Such studies are challenging, often limited by the platform on which the experiment is performed. Using short electrical pulses with rise time ~100ps and pulse widths of the order of 10ns, we are able to probe the switching of the ferroelectric state on timescales much shorter than previous studies. The data reveal low-nanosecond switching, faster than any formerly reported switching times in (La)BFO. We probe the effects of chemical composition on magnetoelectric switching by studying two model systems, namely BFO and La-doped BFO. We study to what extent multiferroic switching conforms to existing models for classical ferroelectric switching and analyze deviations in the context of magnetoelectric coupling. |
Wednesday, March 4, 2020 5:18PM - 5:30PM |
P64.00013: Multiferroic LuFeO3 on GaN, Studies of Band Offsets and a Polar-Polar Interface Joseph Casamento, Darrell Schlom, Huili Grace Xing, Debdeep Jena The ability to integrate epitaxial ferroelectrics on GaN, an established wide bandgap semiconductor platform, has been recently demonstrated [Li et al, Advanced Materials Interfaces 5, 1700921 (2018)] by pulsed laser deposition (PLD) of PbxZr1-xTiO3. LuFeO3, a room temperature ferroelectric and low temperature (~147K) multiferroic material, has been integrated with LuFe2O4 layers in a superlattice that demonstrated near room temperature (~281K) magnetoelectric multiferroic behavior [Mundy et al, Nature 537, 7621 (2016)]. Its hexagonal crystal symmetry makes it promising for epitaxial integration with III-nitrides. Here, we report the molecular beam epitaxy (MBE) growth, ferroelectricity, and band offsets of hexagonal LuFeO3 on GaN. Piezoresponse force microscopy (PFM) results of LuFeO3-n type GaN interface indicate ferroelectric switching behavior. X-ray photoelectron spectroscopy (XPS) of core levels of LuFeO3-GaN interfaces was utilized to determine the valence band offset. Preliminary results indicate a valence band offset of ~1.3 eV. Assuming a bandgap of ~ 1 eV for LuFeO3, this gives a conduction band offset of ~ 1 eV. These studies highlight a potential avenue of epitaxial LuFeO3-GaN based multiferroic-semiconductor heterojunctions for memory and logic applications. |
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