Bulletin of the American Physical Society
APS March Meeting 2011
Volume 56, Number 1
Monday–Friday, March 21–25, 2011; Dallas, Texas
Session B34: Focus Session: Interfaces in Complex Oxides - Spectroscopy and Growth |
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Sponsoring Units: DMP GMAG Chair: John Hill, Brookhaven National Laboratory Room: C141 |
Monday, March 21, 2011 11:15AM - 11:27AM |
B34.00001: Strain-modulated asymmetric orbital--lattice interactions in correlated oxide heterostructures J. Chakhalian, J. Rondinelli , Jian Liu, B. Gray, M. Kareev, E.J. Moon, J. Cohn, M. Varela, S.G. Altendorf, F. Strigari, B. Dabrowski, L.H. Tjeng, P.J. Ryan, J.W. Freeland Artificial structuring of quasi-two dimensional correlated electron thin films and heterointerfaces offers an arena to discover innovative functionalities by harnessing electronic and orbital degrees of freedom. To harness this potential understanding of how structurally linked correlated electronic responses are modified through epitaxial constraints at the substrate--film hetero-interface is clearly required. We use a suite of advanced experimental probes along with ab-initio calculations to show how compressive and tensile bi-axial strain lead to unusual asymmetrical orbital responses. Microscopic studies based on resonant X-ray spectroscopies reveal that the asymmetry leads to a new ground state with a ligand hole density and chemical bond covalency that is modulated by the sign of the epitaxial constraint at the interface. [Preview Abstract] |
Monday, March 21, 2011 11:27AM - 11:39AM |
B34.00002: Structural effects on the electronic properties of epitaxially strained RNiO$_{3}$ thin films I.C. Tung, Jian Liu, B. Gray, J. Chakhalian, J. Rondinelli, P. Ryan, J.W. Kim, M.J. Bedzyk, J.W. Freeland Since the metal--insulator (MI) transition is a hallmark of strongly correlated materials, understanding the behavior of the MI transition of RNiO$_{3}$ (R=rare earth) thin films subjected to confinement, lattice misfit and broken symmetry at the interface in the ultra-thin limit is fundamentally and technologically important [1]. Here we present a study of the effect of the lattice symmetry with epitaxial strain in thin films of LaNiO$_{3}$ and NdNiO$_{3}$ grown on SrTiO$_{3}$(001) substrates by pulsed laser deposition. A combination of x-ray diffraction, soft x-ray absorption spectroscopy, and temperature-dependent resistivity has been applied to elucidate structural and electronic properties of the samples. Work at the Advanced Photon Source, Argonne is supported by the U.S. Department of Energy, Office of Science under Contract No. DE-AC02-06CH11357.\\[4pt] [1] Jian. Liu et al., Appl. Phys. Lett. 96, 233110 (2010). [Preview Abstract] |
Monday, March 21, 2011 11:39AM - 11:51AM |
B34.00003: Orbital engineering near La$_{2}$NiO$_{4}$-La$_{2}$CuO$_{4}$ superlattice interfaces S. Smadici, J.C.T. Lee, J. Morales, P. Abbamonte, G. Logvenov, A. Gozar, I. Bozovic Orbital states of transition metal oxides present the opportunity of adjusting material properties to a specific purpose (orbital engineering). A comparison of the resonant soft x-ray reflectivity of La$_{2}$NiO$_{4}$-La$_{2}$CuO$_{4}$ superlattices at Ni L and Cu L edges shows different spatial distributions of the occupation of Ni d$_{x}$2$_{-y}$2 and d$_{3z}$2$_{-r}$2 orbitals in the LNO layers. This modulation of the Ni valence is possible through a pronounced modulation of the density of oxygen interstitial dopants within the structure which does not follow exactly the structure itself. This is the first observation of orbital engineering in a 214 oxide. [Preview Abstract] |
Monday, March 21, 2011 11:51AM - 12:03PM |
B34.00004: Orbital Control in single unit cell LaNiO3/LaAlO3 superlattices J.W. Freeland, J. Liu, B. Gray, M. Kareev, J.W. Kim, P.J. Ryan, R. Pentcheva, J. Chakhalian Oxide heterostructures built from strongly correlated electron materials offers unique opportunity to generate new ground-states by altering the balance of competing energies in the system. In pursuit of rational control of orbital polarization, we present a combined experimental and theoretical study of single unit cell LaNiO$_3$/LaAlO$_3$ superlattices[1]. Polarized x-ray absorption spectra show a distinct asymmetry in the orbital response under tensile vs. compressive strain. A splitting of orbital energies $\sim$100 meV with octahedral distortions is found for the case of compressive strain which is much smaller than the $3d$ bandwidth. In sharp contrast, for tensile strain, no splitting is found although a strong orbital polarization is still present. Density functional theory calculations of the electronic properties reveal that the asymmetry results from a combination of strain effects and altered covalency in the bonding across the interfacial apical oxygen to the Al site, leading to the opening of a pseudogap in the heterostructure for tensile strain. Work at Argonne, including the Advanced Photon, is supported by the U.S. Department of Energy, Office of Science, and Office of Basic Energy Sciences, under Contract No. DE-AC02-06CH11357. [1] J.W. Freeland et. al. arXiv:1008.5618 [Preview Abstract] |
Monday, March 21, 2011 12:03PM - 12:15PM |
B34.00005: Realistic DMFT calculations for nickelate superlattices M.J. Han, Xin Wang, Chris A. Marianetti, Andrew J. Millis We present phase diagram, photo-emission and RIXS (resonant inelastic X-ray scattering) spectra, orbital polarization, and Fermi surface plots for LaNiO3/LaXO3 superlattice (X=Al, Ga,...) obtained from DMFT (dynamical mean-field theory) calculation based on a realistic multi-band tight-binding model derived from DFT (density functional theory) calculations and in particular including oxygen orbitals. Our results indicate that heterostructuring is unlikely to produce one band model physics and point toward a new view of metal-insulator transition of this system. This work is supported by ARO via grant No. W911NF0910345-56032PH. [Preview Abstract] |
Monday, March 21, 2011 12:15PM - 12:27PM |
B34.00006: Conductivity enhancement of ultrathin LaNiO$_{3}$ films in superlattices Junwoo Son, James M. Lebeau, S. James Allen, Susanne Stemmer The transport properties of heterostructures with Mott materials, such as LaNiO$_{3}$, have been predicted to exhibit unusual phenomena not present in the bulk. Prior studies have shown that ultrathin LaNiO$_{3}$ films exhibit strongly localized behavior, whereas thicker films remain metallic. Here, we report on epitaxial [SrTiO$_{3}$(3 u.c.)/LaNiO$_{3}$(4 u.c.)]$_{n}$ superlattices on (001) (LaAlO$_{3}$)$_{0.3}$(Sr$_{2}$AlTaO$_{6}$)$_{0.7}$ (LSAT) substrates (u.c. = unit cell). X-ray diffraction and Z-contrast imaging confirm sharp interfaces. The sheet resistance of the superlattices is explored as a function of temperature and number of bilayers. All superlattices with more than 2 layers were metallic whereas 4 u.c. LaNiO$_{3}$ films and a single 4 u.c. LaNiO$_{3}$/3 u.c. SrTiO$_{3}$ bilayer were both insulating. The sheet resistance of superlattices decreases with n. Possible models for the electrical characteristics will be discussed. The first model attempts to describe the sheet resistance with conduction through parallel-connected LaNiO$_{3}$ layers and conductive interfacial layers. The second model is based on coupling of layers, each of which is near the percolation threshold for a metal-insulator transition, and explains the difference in conductivity of single layers and superlattices without invoking interfacial layers. [Preview Abstract] |
Monday, March 21, 2011 12:27PM - 12:39PM |
B34.00007: Electric-Field Control of the Metal-Insulator Transition in Nickelate Thin Films Raoul Scherwitzl, Pavlo Zubko, Ignacio Gutierrez-Lezama, Shimpei Ono, Alberto Morpurgo, Gustau Catalan, Jean-Marc Triscone The rare-earth perovskite nickelates (RNiO$_3$) are a fascinating family of compounds displaying a sharp temperature-driven metal-insulator (MI) transition with resistance changes of several orders of magnitude. From a fundamental point of view, these materials present an ideal system to study MI transitions since, in contrast to most oxides, a complete evolution from itinerant to localized behavior can be achieved without doping. From a technological point of view, the nickelates are just as exciting, as the large changes and thermal hysteresis in resistance may find uses in various electronic applications, particularly if the MI transition could be tuned using an electric field. We discuss the electric field control of the MI transition in NdNiO$_3$. The electric double layer technique was used in order to obtain very large charge carrier density modulations (exceeding 10$^{15}$ cm$^{-2}$), enabling us to reversibly tune the transition temperature by more than 50 K and to achieve electro-conductivities as high as 60000\% \lbrack 1\rbrack.\\[4pt] \lbrack 1\rbrack \, R. Scherwitzl \emph{et al.}, Adv. Mater., doi:~10.1002/adma.201003241 (2010) [Preview Abstract] |
Monday, March 21, 2011 12:39PM - 12:51PM |
B34.00008: Interface Structures in Ferromagnetic LaMnO$_{3}$-SrMnO$_{3}$ Superlattices Amish Shah, Quentin Ramasse, Steven May, Anand Bhattacharya, Xiaofang Zhai, James Eckstein, Jian-Min Zuo, John Spence We have investigated the interfaces of LaMnO3$_{2n}$-SrMnO3$_{n}$ (LMO/SMO) superlattices. Charge density calculations have predicted a leakage of Mn e$_{g}$ electrons from LMO into SMO.\footnote{C. Aruta et al., Phys. Rev. B 80 (2009).} For n=1, these electrons are expected to be distributed throughout all films in the superlattice, while for n $>$ 3, the electrons are expected to be localized within a few layers near the interfaces. Using aberration corrected STEM coupled with EELS, we probed a LMO$_{11.8}$-SMO$_{4.4}$ superlattice at high spatial resolution to examine interfacial states. We find that the LMO on SMO interface is structurally sharper than SMO on LMO interfaces. Extra interfacial states above the Fermi level are localized to 1 unit cell of the sharp LMO/SMO interface while the states are weak or absent at the rougher SMO/LMO interfaces. The same interfaces that have extra states have an enhanced ferromagnetic moment at low temperatures.\footnote{S. May et al., Phys. Rev. B 77 (2008).} [Preview Abstract] |
Monday, March 21, 2011 12:51PM - 1:03PM |
B34.00009: Induced Ti magnetism at titanate / manganite interfaces J. Garcia-Barriocanal, F.Y. Bruno, A. Rivera-Calzada, C. Leon, J. Santamaria, J.C. Cezar, P. Thakur, N.B. Brookes, J.W. Taylor, J.A. Duffy, S.B. Dugdale, C. Utfeld, S.R. Giblin, T. Nakamura, K. Kodama, S. Okamoto We show evidence of induced magnetism resulting from the electronic (charge) or orbital reconstruction occurring at the interface. We show a novel form of Ti magnetism at the interface between SrTiO$_{3}$ (STO) and LaMnO$_{3}$ (LMO) [1] as evidenced by evidenced by a strong XMCD signals at Ti and Mn edges. The magnetic alignment (ferromagnetic or antiferromagnetic) of Ti and Mn moments can be tuned by structural parameters. \\[4pt] [1] J. Garcia-Barriocanal et al. Nature Comm. \textbf{1}:82 doi: 10.1038/ncomms1080 (2010) [Preview Abstract] |
Monday, March 21, 2011 1:03PM - 1:39PM |
B34.00010: Orbital Reflectometry and the Electronic Structure of Oxide Interfaces Invited Speaker: The occupation of $d$-orbitals has a key influence on the physical properties of transition-metal (TM) oxides.\footnote{Tokura, Y. $\&$ Nagaosa, N. Science {\bf 288}, 462-468 (2000).} Due to the strong hybridization with neighboring oxygen ions, the electronic structure is very sensitive to changes in the TM-oxygen bond distances induced by strain and/or by the chemical bonding to other ions with different electronic configuration. Both effects might be important in oxide heterostructures,\footnote{Han, M. J., Marianetti, C. A. $\&$ Millis, A. J. Phys.\ Rev.\ B {\bf 82}, 134408 (2010).} but thus far it has been difficult to probe atomic-scale modulations of the orbital occupation in a quantitative manner.\footnote{Chakhalian, J. \textit{et al.} Science {\bf 318}, 1114-1117 (2007).} We present results from polarized soft x-ray resonant reflectivity, which demonstrate that it is possible to derive quantitative, spatially resolved orbital polarization profiles. We show that this method is sensitive enough to resolve differences of $\sim 3\%$ in the occupation of Ni $e_g$ orbitals in adjacent atomic layers of a LaNiO$_3$-LaAlO$_3$ superlattice, and the experimental findings are in good agreement with electronic-structure calculations. The possibility to quantitatively correlate theory and experiment on the atomic scale opens up new perspectives for orbital physics in oxide heterostructures. [Preview Abstract] |
Monday, March 21, 2011 1:39PM - 1:51PM |
B34.00011: Source oxidation problem in oxide-MBE environment and its solution Namrata Bansal, Yong-Seung Kim, Seongshik Oh Maintaining stable fluxes for multiple source elements is a challenging task when the source materials have significantly different oxygen affinities in a complex-oxide MBE environment. Although this problem has been known to the complex oxide MBE community since the late 1980s, a detailed study and solution is still lacking. Here, using Sr as a test source, because of its easy oxidation and popularity in complex oxides, we investigated the source-oxidation problem in a number of different conditions. We found that the source oxidation was less for higher flux rates, unmelted source shape, and extended port geometry. The extended port geometry was also found to eliminate the flux transient, usually observed in a standard port, after opening the source shutter. Furthermore, a crucible aperture insert scheme was found to be very effective in suppressing the source oxidation. In this scheme, a disk-shaped aperture was mounted inside the crucible and we found that it blocks most of the oxygen species coming to the source. However, the depth of the aperture disk was critical for its performance. We will discuss how these configurations suppress source oxidation and lead to significantly enhanced stability of Sr-flux in harsh oxidation conditions. [Preview Abstract] |
Monday, March 21, 2011 1:51PM - 2:03PM |
B34.00012: Growth of SrTiO3(110) film with oxide molecule beam epitaxy Jiandong Guo, Zhiming Wang, Fang Yang, Jiagui Feng, Fengmiao Li In the past decade, a tremendous amount of evidence has shown that thin films, superlattices and heterointerfaces of oxides display a rich diversity of glamorous properties that is related, but not identical to that in the bulk. To understand the underlying physical mechanism, it is essential to construct the oxide heterostructures under control with atomic precision. We have studied the SrTiO$_{3}$(110) surface that bears intrinsic instability of reconstruction in addition to the broken symmetry due to the surface polarity, which provides us an additional degree to tune the properties of the epitaxial material by manipulating the termination layer of the substrate. Beyond the termination, we are able to tune the stability of a series of surface reconstructions and realize the reversible phase transitions between them. By applying the knowledge to the homoepitaxy, we develop an easy method to coordinate the metal evaporation sources with required flux rate ratio precisely during the oxide MBE growth. We further simplify the growth by controlling the shutter of the Sr source. The atomically well defined grown surface is characterized by scanning tunneling microscopy. [Preview Abstract] |
Monday, March 21, 2011 2:03PM - 2:15PM |
B34.00013: Oxygen Doping Study of Cuprate/Manganite Thin-Film Heterostructures Hao Zhang, J.Y.T. Wei, Wen He Gong, Gianluigi A. Botton Recent studies of thin-film heterostructures comprising superconducting cuprates and ferromagnetic manganites have revealed a range of novel physical phenomena. These phenomena are believed to involve complex interfacial interactions between competing order parameters [1], and appear to be highly sensitive to carrier doping [2]. To further examine these phenomena, we carry out a systematic oxygen-doping study of cuprate/manganite multilayer thin films, grown epitaxially by pulsed laser-ablated deposition. Our samples are characterized by electrical transport and magnetization measurements, as well as x-ray diffraction and several microscopy probes including SEM and TEM. We also make cation substitution in the cuprate layer, in order to study the effects of carrier doping across the interface.\\[4pt] [1] For example, see J. Hoppler \textit{et al.}, Nature Materials \textbf{8}, 315 (2009).\\[0pt] [2] V. Pe\~{n}a \textit{et al.}, Phys. Rev. Lett. \textbf{97}, 177005 (2006). [Preview Abstract] |
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