Bulletin of the American Physical Society
2009 APS March Meeting
Volume 54, Number 1
Monday–Friday, March 16–20, 2009; Pittsburgh, Pennsylvania
Session Q30: Focus Session: Oxide Superlattices |
Hide Abstracts |
Sponsoring Units: DMP GMAG Chair: Maria Varela, Oak Ridge National Laboratory Room: 334 |
Wednesday, March 18, 2009 11:15AM - 11:27AM |
Q30.00001: Colossal ionic conductivity at ZrO$_{2}$:Y$_{2}$O$_{3}$ /SrTiO$_{3}$ interfaces Jacobo Santamaria, J. Garcia Barriocanal, A. Rivera Calzada, Z. Sefrioui, C. Leon, E. Iborra, M. Varela, S.J. Pennycook We describe the strong enhancement of the conductivity occurring at the interfaces of superlattices made by alternating 10 nm strontium titanate and 1 nm yttria stabilized zirconia $^{[1]}$layers. Conductivity is found to be as high as 0.014 S/cm at 357 K, with a substantial decrease of the activation energy for the dc ionic conductivity from 1.1 eV down to 0.64 eV. EELS analysis is consistent with a large number of interfacial oxygen vacancies and high disorder in the interface oxygen plane between YSZ and STO layers. Our results demonstrate that the design of suitable heterogeneous interfaces in epitaxial heterostructures might have important implications in the search of artificial nanostructures with high ionic conductivity. Work at UCM and UPM supported by MCINN MAT2008 6517and Division of Materials Sciences and Engineering of the US Department of Energy. [1] J. Garcia-Barriocanal, et al. Science \textbf{\textit{321}}, 676 (2008) [Preview Abstract] |
Wednesday, March 18, 2009 11:27AM - 11:39AM |
Q30.00002: Origin of Colossal Ionic Conductivity in YSZ-STO Superlattices Timothy Pennycook, Matthew Beck, Kalman Varga, Maria Varela, Stephen Pennycook, Sokrates Pantelides An eight order of magnitude increase in the ionic conductivity of yttria-stabilized zirconia (YSZ) has recently been demonstrated in YSZ/strontium titanate (STO) epitaxial heterostructures. YSZ is the preferred electrolyte for solid oxide fuel cells (SOFC), in which the ionic conductivity is the major factor limiting the energy conversion efficiency. A colossal increase in the ionic conductivity, therefore, goes a long way towards increasing SOFC practicality by increasing efficiency overall and reducing the operating temperature necessary for efficient operation. We report density functional calculations that explain this colossal ionic conductivity as the result of a large 7\% expansive in-plane strain of the YSZ. Molecular dynamics simulations of strained zirconia yield an activation energy for ionic conduction in agreement with experiment. Additionally, simulated annealing under these strain conditions reveals a new lowest energy structure for which EELS simulations using the Z+1 approximation for the core hole are consistent with electron energy loss spectra from the thin, coherently strained, YSZ layers of the heterostructures. This work is supported by NSF grant DMR-0513048 and DOE Office of Basic Energy Sciences, Division of Materials Science and Engineering. [Preview Abstract] |
Wednesday, March 18, 2009 11:39AM - 11:51AM |
Q30.00003: Non-uniform magnetization in LaAlO$_{3}$/SrTiO$_{3}$ superlattices. M.R. Fitzsimmons, M. Zhernenkov, N. Hengartner, A. Sharoni, Ivan K. Schuller, J. Garcia-Barriocanal, F.Y. Bruno, J. Santamaria Recently, Brinkman et al., [Nature \textbf{6}, 493 (2007)] reported magnetism induced at the interface between LaAlO$_{3}$ (LAO) and SrTiO$_{3 }$(STO)$_{ }$inferred from transport measurements. They found the magnetization to be greatly enhanced at low temperatures (i.e., liquid He temperature) and by application of high (10+ T) fields. We report polarized neutron reflectometry measurements of the magnetization depth profile of two LAO/STO superlattices with the same number of bilayer repeats. For low temperatures and a field of 11 T, the intensities of the superlattice Bragg reflections for both samples exhibited a dependence upon neutron beam polarization. The spin dependence was much weaker at small field (and low temperature) and disappeared altogether at 11 T and 300 K. These observations demonstrate that the magnetization depth profile has the period of the LAO/STO superlattice. The neutron spin dependence was more pronounced for the sample with a thin LAO layer compared to one with a thick LAO layer, suggesting that the magnetism may be interfacial in origin. [Preview Abstract] |
Wednesday, March 18, 2009 11:51AM - 12:27PM |
Q30.00004: How to make a cuprate Fermi surface out of a nickelate heterostructure Invited Speaker: Chaloupka and Khaliullin had the idea that it might be possible to make Ni$^{3+}$-based high-temperature superconductors by sandwiching NiO$_{2}$ layers between insulating layers through heterostructuring.$^{2}$ Provided that spin-, charge-, and orbital ordering can be avoided, the confinement should make it possible to empty the Ni $3z^{2}-1$ band, thus leaving the conduction electron in the Ni $x^{2}-y^{2}$ band. Fabrication of such heterostructures are now being pursued in many laboratories. We$^{3}$ have attempted to give theoretical guidance by performing calculations for numerous heterostructures using the local density-approximation in combination with static (LDA+U) and dynamical (LDA+DMFT) mean-field theory. We show how confinement together with electronic correlations can lead to a single-sheet Fermi surface with a shape like that of the cuprate superconductors with the highest transition temperatures$;$ the Ni $3z^{2}-1$ Wannier orbital now plays the role of the axial, Cu $4s$-like orbital in the cuprates.$^{4}$ Since also strong antiferromagnetic fluctuations are present, the low-energy electronic and spin excitations should resemble those of high-temperature cuprate superconductors. Chemical modification of the insulating layers should make it possible to avoid spin-, charge-, and orbital ordering.\newline $^{2}$J. Chaloupka and G. Khaliullin, Phys. Rev. Lett. \textbf{100,} 016404 (2008).\newline $^{3}$P. Hansmann, Xiaoping Yang, A. Tosci, G. Khaliullin, O.K. Andersen, and K. Held, arXiv: 0807.0407.\newline $^{4}$E. Pavarini, I. Dasgupta, T. Saha-Dasgupta, O. Jepsen, and O. K. Andersen, Phys. Rev. Lett. \textbf{87}, 047003 (2001). [Preview Abstract] |
Wednesday, March 18, 2009 12:27PM - 12:39PM |
Q30.00005: Interfaces in $\rm La_{2}NiO_{4} - La_{2}CuO_{4}$ superlattices S. Smadici, J. C. T. Lee, S. Wang, P. Abbamonte, G. Logvenov, A. Gozar, I. Bozovic Ni substitution on Cu sites in underdoped $\rm La_{2-x}Sr_{x} CuO_{4}$ quickly restores Neel order. This was attributed to strong interaction between the Ni and doped holes. An open question was whether the additional Ni empty orbital or the different spin on Ni sites was at the origin of this strong interaction. We have addressed this problem with resonant soft x-ray scattering on a $\rm La_{2}NiO_{4} - La_{2}CuO_{4}$ heterostructure. $\rm La_{2}NiO_{4}$ and $\rm La_{2}CuO_{4}$ have close lattice structures and electronic configurations. However, the x-ray scattering contrast between superlattice layers is greatly enhanced at soft x-ray resonant energies. Based on our measurements at the O K, La M, Cu L and Ni L edges a model of the charge, orbital and spin structures in these superlattices will be presented with a special emphasis on the interface region. This work was supported by Grants. DE-FG02- 06ER46285, DE-AC02-98CH10886, MA-509-MACA, DE-FG02-07ER46453 and DE-FG02-07ER46471. [Preview Abstract] |
Wednesday, March 18, 2009 12:39PM - 12:51PM |
Q30.00006: Layer-by-layer growth by pulsed laser deposition in the unit-cell limit. M. Kareev, S. Prosandeev, J. Liu, P. Ryan, J.W. Freeland, J. Chakhalian Unlike conventional growth of complex oxide heterostructures, the ultimate unit cell limit imposes strict constrains for a multitude of parameters critical to layer-by-layer growth. Here we report on detailed analysis of far-from-equilibrium growth by interrupted pulsed laser deposition with application to RENiO$_{3}$/LaAlO$_{3 }$superlattices grown on a diverse set of substrates SrTiO$_{3}$, NdGaO$_{3}$, LSAT and LaAlO$_{3}$. A combination of \textit{in-situ} high-pressure RHEED and AFM along with extensive data obtained from synchrotron based XRD and resonant XAS allows us critically assess the meaning of RHEED intensity oscillation and the effect of a polar/non-polar interface on the heteroepitaxial growth. The role of defects formed during the initial stages of growth is also addressed. [Preview Abstract] |
Wednesday, March 18, 2009 12:51PM - 1:03PM |
Q30.00007: Perfect dc conductance of a finite width Mott insulator sandwiched between metallic leads at zero temperature: a quantum emergent phenomenon in strongly correlated multilayers Hand Zenia, Jim Freericks, Hulikal Krishnamurthy, Thomas Pruschke Self-consistent inhomogeneous DMFT calculations as well as analytical investigations of the electronic structure of a multilayered device are presented. The device consists of two semi-infinite leads of a ballistic metal that sandwich an interacting barrier. The interactions in the barrier are described by the Hubbard model with the whole system particle-hole symmetric. We find that for a finite barrier no matter how strong the interaction, the system becomes a Fermi liquid with a perfect metallic conductivity at low enough temperature. We argue that at zero temperature and frequency the Luttinger theorem holds and that the system has a well defined Fermi surface. The perfect conducting state may be extremely fragile to finite temperature, finite driving electric fields, finite driving frequencies, or disorder, so it will often be difficult to see experimentally. We will discuss possible experimental realizations of the phenomena [Preview Abstract] |
Wednesday, March 18, 2009 1:03PM - 1:39PM |
Q30.00008: Strongly Interacting Electrons at the Oxide Interfaces. Invited Speaker: Utilizing the recent advances in complex oxide synthesis, one can now combine materials with antagonistic order parameters to create new compounds in the form of heterostructures often with properties not attainable in the bulk$^{1}$. Broken symmetries, strain, and modified local environment at the interface provide a unique route to manipulate the subtle energy balance in correlated materials with promise to create novel material phases and quantum states. Here we report on how the interface can be used to alter electronic, magnetic and orbital structure of multilayers composed of late transition metal oxides with specific examples from cuprates, manganites and nickelates. We will discuss the underlying challenges in growth of ultra-thin layers of complex oxides and illustrate the ways synchrotron based resonant x-ray spectroscopies and resonant x-ray diffraction can be used to probe bulk vs. interface properties to gain unique insight into the underlying physics. J. Chakhalian et al, Science, v. 314, 1114, (2007). [Preview Abstract] |
Wednesday, March 18, 2009 1:39PM - 1:51PM |
Q30.00009: X-ray standing wave photoemission from multilayer nanostructures C. Papp, B. Balke, C. Sakai, S. Ueda, H. Yoshikawa, Y. Yamashita, S. L. He, K. Kobayashi, G. Conti, D. Buergler, C. Schneider, C. S. Fadley, S. Doering, U. Berges, C. Westphal We have used soft and hard x-ray standing wave excitation of photoelectrons to study buried layers and interfaces in multilayer nanostructures. The samples were grown on synthetic multilayer mirrors, and the x-ray incidence was tuned to 1$^{st}$ order Bragg reflection. Scanning angle, photon energy, or distance along a wedge profile in the sample permits scanning the resultant standing wave field through nm-scale structures and analyzing the depth distribution of their chemical, electronic, magnetic, and structural properties. Using harder x-ray excitation permits via the higher kinetic energy of the electrons studying those properties at greater depths. The systems discussed will be two related to magnetic tunnel junctions (magnesium oxide/iron and STO/LSMO), and one related to integrated circuit production (titanium nitride on silicon). [Preview Abstract] |
Wednesday, March 18, 2009 1:51PM - 2:03PM |
Q30.00010: Competing anisotropies and complex magnetism in SrRuO$_{3}$/SrMnO$_{3}$ superlattices Omar Chmaissem, Y. Choi, Y.C. Tseng, D. Haskel, D.E. Brown, S. Kolesnik, D. Danaher Using element-specific x-ray resonance techniques, we have investigated the interfacial magnetic coupling in SrRuO$_{3}$/SrMnO$_{3}$ superlattices. A strong out-of-plane SRO anisotropy coupled with AFM Ru-Mn interactions result in a canted Mn structure with a significant induced net Mn moment that reduces to zero under a strong magnetic field. At T $>$ T$_{C SRO}$, the SRO anisotropy is removed and the planar Mn AFM structure cants to produce a net Mn moment along the field direction. Below T$_{C}$, the net development of in-plane Mn moment is suppressed by partially frustrated exchange interactions at the AFM-SMO/FM-SRO interfaces and competing Mn-Ru anisotropies. Hysteretic magnetization curves show a two-step magnetization reversal and enhanced coercivity. X-ray measurements confirm that the low-field magnetization reversal coincides with ``free'' Ru moments inside the SRO layers and that the high-field magnetization reversal involves the interfacial magnetization in the SMO layers and provide strong evidence for the presence of pinned SRO moments at the SRO/SMO interface. [Preview Abstract] |
Wednesday, March 18, 2009 2:03PM - 2:15PM |
Q30.00011: Electrically controlled magnetization in tricolor superlattices Jaekwang Lee, Na Sai, Alexander A. Demkov With recent breakthroughs in fabricating high-quality oxide films, ultra thin ferroelectric (FE) films have attracted significant attention. Many FE-based electronic devices proposed to date have a capacitor configuration, where a FE layer is inserted between two identical metal electrodes. We consider theoretically so-called tricolor structures or asymmetric capacitors with one electrode being ferromagnetic and other normal metal. An interesting aspect of a tricolor structure is breaking of the inversion symmetry which is expected to generate new properties. Of particular interest is the control of the magnetization in a ferromagnetic layer without using an external magnetic field. The effect may find applications in low-power and high-density integration in future spintronics devices. To investigate the polarization-dependent magnetization change in the iron layer we construct the tricolor superlattices comprised of Fe/BaTiO$_{3}$/Pt, Fe/PbTiO$_{3}$/Pt and perform first principles calculations at the LSDA+U level. We find the electrode magnetization sensitive to the polarization direction in the FE layer, which suggests a multiferroic character of the structure. The effect is much stronger than in the analogous symmetric structures. [Preview Abstract] |
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. |
© 2025 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