Bulletin of the American Physical Society
APS March Meeting 2014
Volume 59, Number 1
Monday–Friday, March 3–7, 2014; Denver, Colorado
Session D49: Focus Session: Nickelate Heterostructures |
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Sponsoring Units: DMP Chair: Stephen Wilson, Boston College Room: Mile High Ballroom 1C |
Monday, March 3, 2014 2:30PM - 3:06PM |
D49.00001: Characterization and control of orbital, spin and charge order in nickel oxide superlattices Invited Speaker: Bernhard Keimer This talk will provide an overview of spectroscopic experiments on the structural [1,2] and electronic [3-7] properties of nickel oxide superlattices grown by pulsed laser deposition and molecular beam epitaxy. We will discuss recent progress in the quantitative characterization of the Ni d-orbital polarization as a function of epitaxial strain, spatial confinement, and chemical composition [4,5] and discuss its influence on spin [6] and charge [7] order in these systems. The power of spectroscopic methods such as resonant x-ray scattering, spectral ellipsometry, and Raman scattering for the characterization of electronic ordering phenomena in metal-oxide heterostructures and superlattices will be emphasized. \\[4pt] [1] E. Detemple et al., Appl. Phys. Lett. 99, 211903 (2011).\\[0pt] [2] A. Frano et al., Adv. Mater. (2013); doi: 10.1002/adma.201303483.\\[0pt] [3] A.V. Boris et al., Science 332, 937 (2011).\\[0pt] [4] E. Benckiser et al., Nature Mater. 10, 189 (2011).\\[0pt] [5] M. Wu et al., Phys. Rev. B 88, 125124 (2013).\\[0pt] [6] A. Frano et al., Phys. Rev. Lett. 111, 106804 (2013).\\[0pt] [7] A. Frano, M. Hepting et al., unpublished. [Preview Abstract] |
Monday, March 3, 2014 3:06PM - 3:18PM |
D49.00002: Anti-ferromagnetically driven Mott transition in ultrathin nickelates Derek Meyers, Jian Liu, M. Kareev, S. Middey, J.W. Freeland, R. Averitt, A.J. Millis, P. Ryan, J. Chakhalian The independent roles of anti-ferromagnetism and charge ordering in the realization of the temperature induced Mott metal-to-insulator transition within heteroepitaxial nickelate films remain to be disentangled hindering true understanding of the nature of the still actively debated ground state. To this end, we have investigated ultra thin, fully epitaxial films of the strongly correlated electron system NdNiO$_{3}$ by hard and soft resonant x-ray scattering. We find a robust E'-type antiferromagnetic transition, analogous to the bulk ordering, occurs despite the ultra thin nature of the films. Surprisingly, no evidence of a symmetry change was found upon cooling below the metal-to-insulator transition utilizing multiple probes. Supporting theoretical calculations show the anti-ferromagnetic transition corroborates with the opening of the charge excitation gap. [Preview Abstract] |
Monday, March 3, 2014 3:18PM - 3:30PM |
D49.00003: ABSTRACT WITHDRAWN |
Monday, March 3, 2014 3:30PM - 3:42PM |
D49.00004: Tuning the metal-insulator transition temperature of Sm$_{0.5}$Nd$_{0.5}$NiO$_{3}$ thin films via strain H. Jeffrey Gardner, Vijay Singh, Le Zhang, Xia Hong We have investigated the effect of substrate induced strain and film thickness on the metal-insulator transition of the correlated oxide Sm$_{0.5}$Nd$_{0.5}$NiO$_{3}$ (SNNO). We have fabricated epitaxial 3 -- 40 nm thick SNNO films on (001) LaAlO$_{3}$ (LAO), (001) SrTiO$_{3}$ (STO), and (110) NdGaO$_{3}$ (NGO) via off-axis RF magnetron sputtering. The SNNO films are atomically smooth with (001) orientation as determined by atomic force microscopy and x-ray diffraction. SNNO films grown on LAO, subject to compressive strain, exhibit a sharp metal-insulator transition at lower temperatures. Conversely, films grown on STO and NGO, subject to tensile strain, exhibit a smeared albeit above room temperature metal-insulator transition. For all substrates, we have observed that the metal-insulator transition temperature ($T_{MI})$ increases monotonically with decreasing film thickness until the electrically dead layer is reached (below 4 nm). We discuss the effect of strain and oxygen deficiencies on the T$_{MI}$ of SNNO thin films. [Preview Abstract] |
Monday, March 3, 2014 3:42PM - 3:54PM |
D49.00005: A structural route to tuning the orbital structure of nickelates Divine Kumah, Ankit Disa, Andrei Malashevich, Hanghui Chen, Sohrab Ismail-Beigi, Fred Walker, Charles Ahn The rare-earth nickelates display a range of interesting magnetic and electronic phenomena arising from the strong coupling of the atomic-scale structural properties of these systems to the charge and orbital degrees of freedom. We report on modifying the orbital polarization in nickelate based heterostructures, motivated by the goal of emulating high-Tc cuprate behavior in the nickelates. Using a combination of synchrotron diffraction structural and spectroscopic characterization and first principles theory, we show how the design of a structure that splits the relative electronic occupation of Ni d x$^{2}$-y$^{2}$ and Ni d 3z$^{2}$-r$^{2}$ orbitals, is achieved in three-component heterostructures. These structures are comprised of LaTiO$_{3}$/LaNiO$_{3}$/LaAlO$_{3}$ and are grown using molecular beam epitaxy. The key features of the theoretically proposed structure, including an internal polar field, a electron transfer from Ti to Ni, and a orbital polarization of the Ni-eg states, are experimentally studied. [Preview Abstract] |
Monday, March 3, 2014 3:54PM - 4:06PM |
D49.00006: Modulating the properties of thin film nickelates using a ferroelectric Matthew S. J. Marshall, Andrei Malashevich, Ankit S. Disa, Hanghui Chen, Sohrab Ismail-Beigi, Fred J. Walker, Charles H. Ahn Controlling materials properties using electric fields is an important approach to creating novel electronic materials. The perovskite oxides, which exhibit some of the most interesting phenomena found in the solid state, represent an ideal system for exploring how electric fields couple to material properties. As an example, the rare-earth nickelates (LaNiO$_{\mathrm{3}}$, NdNiO$_{\mathrm{3}}$, etc.) undergo a metal-insulator transition when the unit cell structure is changed by chemical doping or through the application of strain. Here we show that the polarization of the canonical ferroelectric PbZr$_{\mathrm{0.2}}$Ti$_{\mathrm{0.8}}$O$_{\mathrm{3\thinspace }}$couples to the structure and conductivity of the rare earth nickelates (RNiO$_{\mathrm{3}})$. As the polarization of the PZT is switched, we introduce atomic-scale structural distortions at the PZT-nickelate interface that modulate the carrier concentration in the nickelate. We find that interfacial effects dominate, resulting in a large change in the conductivity of the nickelate. [Preview Abstract] |
Monday, March 3, 2014 4:06PM - 4:18PM |
D49.00007: Field-effect modulation of structure and carrier transport of LaNiO$_3$ thin films Andrei Malashevich, Matthew S.J. Marshall, Ankit S. Disa, Frederick J. Walker, Charles H. Ahn, Sohrab Ismail-Beigi Materials exhibiting large changes in resistivity in response to applied electric fields are of importance due to their technological applicability, e.g., in field-effect transistors. Of particular interest are thin film oxide/ferroelectric interfaces: the ferroelectric permits dynamic modulation of electronic transport in the oxide film which is crucial for non-volatile memory applications. In the standard field effect, resistance modulations result from changes in carrier density created by the applied electric field. At ferroelectric interfaces, however, other mechanisms can come into play. Our experiments show that at the (001) interface of rare-earth nickelates and ferroelectric Pb$_{0.8}$Zr$_{0.2}$TiO$_3$ (PZT), the change of carrier mobility plays a critical role in the electronic transport. Here, we present a first-principles study of the interface between a thin film of conducting LaNiO$_3$ and ferroelectric PbTiO$_3$ (PTO). We analyze the dependence of the atomic structure of the interface on the PTO polarization and the effect of the structural changes on the electronic bands and associated carrier transport. We also describe the methodological challenges in transport calculations of metal/ferroelectric interfaces and some ways to address them. [Preview Abstract] |
Monday, March 3, 2014 4:18PM - 4:30PM |
D49.00008: Tailoring polarity in a layered nickelate with single atomic layer control Anand Bhattacharya, Brittany Nelson-Cheeseman, Hua Zhou, Prasanna Balachandran, Gilberto Fabbris, Jason Hoffman, Daniel Haskel, James Rondinelli Many of the 3d transition metal oxides share a common structural MO$_{\mathrm{6}}$ building unit---a central transition metal (TM) cation octahedrally coordinated with oxygen nearest neighbors. The electronic states in these materials can be modified by tailoring the M-O bonds, which typically include the application of epitaxial strain in thin films, or pressure and isovalent cation substitution in bulk samples. Here, we present a new route to tailor the M-O bonds without changes to the strain state or stoichiometry in two-dimensional perovskite nickelate (n$=$1 in the Ruddlesden Popper series). We do this by tailoring the dipolar electrostatic interactions at the unit cell level in nominally non-polar LaSrNiO$_{\mathrm{4}}$ via single atomic layer-by-layer synthesis using oxide-MBE. We reconstruct the response of the crystal lattice to the induced polarity using a x-ray phase retrieval technique (COBRA). We find that the response of the O anions to the resulting local electric fields distorts the M-O bonds, being largest for the apical oxygens (O$_{\mathrm{ap}})$. It also alters the Ni valence. [Preview Abstract] |
Monday, March 3, 2014 4:30PM - 4:42PM |
D49.00009: Effect of Polar Discontinuity on the Growth of Epitaxial LaNiO$_3$ Ultrathin Films I.-Cheng Tung, G. Luo, D. Morgan, J.H. Lee, H. Hong, S.H. Chang, J.A. Eastman, D.D. Fong, M.J. Bedzyk, J.W. Freeland We have conducted a detailed microscopic study of epitaxial LaNiO$_3$ ultrathin films grown on (001) SrTiO$_3$ as a function of thickness by using oxide molecular beam epitaxy with in-situ surface x-ray diffraction and soft x-ray absorption spectroscopy at the Advanced Photon Source to explore the influence of polar mismatch on the resulting structural and electronic properties. Our data demonstrate that the initial layers on the nonpolar SrTiO$_3$ surface exhibit a smaller than expected out-of-plane lattice-spacing with a Ni valence of 2+. As the film becomes thicker, the lattice constant expands to its elastic limit, and the Ni valence approaches 3+. We will also discuss the energetics for vacancy formation during the initial growth as determined by density functional theory calculations. Work at the APS, Argonne is supported by the U.S. Department of Energy, Office of Science, and Office of Basic Energy Sciences, under Contract No. DE-AC02-06CH11357. [Preview Abstract] |
Monday, March 3, 2014 4:42PM - 4:54PM |
D49.00010: Polar compensation in ultrathin films of a perovskite nickelate S. Middey, P. Rivero, D. Meyers, M. Kareev, X. Liu, Y. Cao, J.W. Freeland, S. Barraza-Lopez, J. Chakhalian The effect of strong polarity mismatch at the heterointerface, grown along the pseudo cubic [111] direction between the correlated metal LaNiO$_{3}$ and band insulator SrTiO3 has been considered. While the metallic LaNiO$_{3}$ film can itself screen this polarity mismatch, additional reconstruction mechanisms are needed in ultrathin films which are insulating in nature. The reflection high energy electron diffraction patterns recorded during growth highlighted the evolution of nucleation of an additional phase during the first few unit cells of deposition, which are found to be oxygen deficient phase LaNiO$_{\mathrm{3-x}}$ by x ray diffraction and x-ray resonant spectroscopy measurement. The amount of oxygen vacancies decreases ABRUPTLY with the increase of film thickness due to the increase electrical conductivity, which acts in a partial screening of the polar catastrophe. [Preview Abstract] |
Monday, March 3, 2014 4:54PM - 5:06PM |
D49.00011: Observation of strain-controlled electronic modulations revealed by Fermi surface superstructures in strongly correlated LaNiO$_{3}$ films Hyangkeun Yoo, Seungill Hyun, Luca Moreschini, Hyeong-do Kim, Youngjun Chang, Changhee Sohn, Dawoon Jeong, Soobin Sinn, Yongsu Kim, Aaron Bostwick, Eli Rotenberg, Jihoon Shim, Taewon Noh Control over the electronic properties of strongly correlated electron systems can be achieved by exploiting the misfit strain that exists in epitaxial films on lattice mismatched substrates. Here, we report a systematic investigation of electronic structures in strongly correlated LaNiO$_{3}$ films under different strain states, using \textit{in situ} angle-resolved photoemission spectroscopy and the dynamical mean field theory. LaNiO$_{3}$ film shows a change of a Fermi surface (FS) topology, driven by interplay between strong electron-electron correlations and misfit strain effects. Additionally, different from compressive strain case, a FS with tensile strain has a large flat region to induce strong FS nesting. As a result, different FS superstructures are observed in the compressive and tensile strain cases, and their origins are attributed to charge disproportionation and spin density waves, respectively. The more details will be discussed in the presentation. [Preview Abstract] |
Monday, March 3, 2014 5:06PM - 5:18PM |
D49.00012: Atomic Resolution Strain Analysis of Oxide Superlattices Ji-Hwan Kwon, Jason Hoffman, Anand Bhattacharya, Jian-Min Zuo Measuring strain inside the heteroepitaxial transition metal oxide superlattices is critically important, as strain controlled by composition has a large impact on the superlattice properties. Because of the small periods in oxide superlattices, strain analysis must be performed at atomic resolution in order to examine, for example, how strain changes across the interface, whether strain is uniform inside oxide layers or it varies from intermixing between the constituent materials. Strain analysis also provides structural information of the heteroepitaxial superlattice. In this study, we examined the strain in LaNiO$_{\mathrm{3}}$(LNO)/LaMnO$_{\mathrm{3}}$(LMO) superlattice thin films grown on SrTiO$_{\mathrm{3}}$ substrate with a spatial resolution of a single perovksite unit cell using template matching method based on the Z-contrast image. The LNO/LMO interface is hard to be determined by Z-contrast imaging alone due to the same element occupation for A-site and the similar atomic number Z for B-site (Mn and Ni). However, strain analysis reveal sharp interfaces between LNO and LMO layer, in which LNO layers are subjected to tensile strain while LMO layers to compressive strain, showing alternating epitaxial strain inside the superlattice. The detailed analysis including strain variation depends on number of LNO layer and associated deviation of B-site position will be presented. [Preview Abstract] |
Monday, March 3, 2014 5:18PM - 5:30PM |
D49.00013: Laser MBE for atomic layer by layer growth of LaNiO$_{3}$ films and superlattices from separate oxide targets Maryam Golalikhani, Qingyu Lei, Pasquale Orgiani, Xiaoxing Xi Laser MBE was used to grow Nickelate thin films and superlattices in atomic layer by layer manner from separate oxide targets. Stoichiometry and full layer coverage was controlled by in-situ monitoring of Reflection High Energy Electron Diffraction (RHEED) intensity oscillation. LaNiO$_{3}$ ultra-thin films were grown from La$_{2}$O$_{3}$ and NiO targets on LaAlO$_{3}$ and SrTiO$_{3}$ substrates. X-ray diffraction, x-ray reflectivity, and atomic force microscopy were used to characterize the structure, thickness, and surface morphology of the films. The origin of thickness dependent metal to insulator transition was studied using the transport properties and x-ray absorption spectroscopy measurements. Single unit cell LaNiO$_{3}$/LaAlO$_{3}$ superlattices were grown from La$_{2}$O$_{3}$, NiO and Al$_{2}$O$_{3}$ targets on LaAlO$_{3}$ substrate. By means of polarization-dependent x-ray Absorption Spectroscopy, orbital ordering in these supperlattices was studied and the results are presented herein. [Preview Abstract] |
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