Bulletin of the American Physical Society
2005 APS March Meeting
Monday–Friday, March 21–25, 2005; Los Angeles, CA
Session B3: DCMP/DMP Joint Prize Session |
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Sponsoring Units: DCMP Chair: Samuel Bader, Argonne National Lab and Sidney Nagel, University of Chicago Room: LACC 515B |
Monday, March 21, 2005 11:15AM - 11:51AM |
B3.00001: Valley Prize Talk Invited Speaker: Intuitively, electrons in metals are ``free,'' while in insulators they are ``bound,'' or ``localized.'' This is why under a dc bias metals carry a steady current and insulators acquire an electric polarization. What is the precise nature of this localization, in view of the fact that the charge density can be as delocalized in a covalent crystal as in a metal? I will discuss a rigorous notion of localization in the insulating state, and how it relates to both the extended (``band'') and the localized (``bond'') pictures of electrons in solids. It is closely tied to the finding that a knowledge of the bulk charge density alone is not sufficient to define the dielectric polarization. Instead, this quantity is given by a global phase property (Berry's phase) of the Bloch states in the filled bands or, alternatively, by the centers of charge of the occupied Wannier orbitals. Similarly, electron localization in insulators is not a property of the charge density. It is instead related to the spatial extent of the Wannier orbitals, and describes the quantum fluctuations of the ground state polarization. These ideas have had a practical impact on {\it ab initio} studies of the dielectric properties of real materials. For example, they have led to a method for applying finite electric fields to insulators without resorting to artificial sawtooth potentials. [Preview Abstract] |
Monday, March 21, 2005 11:51AM - 12:27PM |
B3.00002: Maria Goeppert-Mayer Award Talk: Novel Magnetism and Transport in Complex Oxide Thin Films, Multilayers and Nanostructures Invited Speaker: Yuri Suzuki In epitaxial complex oxide systems, epitaxial strain, cation substitution and nanofabrication are just some ways in which their magnetic, electronic and optical properties may be tuned. In addition, their surfaces and interfaces provide a rich playground for the exploration of novel magnetic properties not found in the bulk constituents and the development of functional interfaces to be incorporated into technological applications. We have probed magnetism in complex oxide materials through studies of epitaxial oxide thin films, nanostructures and junction devices. With our ability to control oxide film growth as well as our expertise in nanofabrication, we have been able to study the effects of surfaces and interfaces on magnetism in ultra-thin magnetic oxide films and magnetic oxide nanostructures. For example, we have found that the nature of local magnetic structure in submicron islands of colossal magnetoresistance (CMR) material reveals the importance of shape anisotropy as well as magnetostriction in determining the micromagnetics in such small CMR structures. We have also studied epitaxial oxide trilayer junctions composed of magnetite (Fe$_{3}$O$_{4})$ and doped manganite (La$_{0.7}$Sr$_{0.3}$MnO$_{3})$ in which we have confirmed the theoretically predicted negative spin polarization of Fe$_{3}$O$_{4}$. Transport through the barrier can be understood in terms of hopping transport through localized states that preserves electron spin information. [Preview Abstract] |
Monday, March 21, 2005 12:27PM - 1:03PM |
B3.00003: Davisson-Germer Award Talk: Surface Electron Microscopy with Slow Electrons Invited Speaker: Nearly 80 years ago Davisson and Germer demonstrated the diffraction of slow electrons from surfaces but it is only about 20 years that these electrons have been used for imaging of surfaces and thin films in the Low Energy Electron Microscope (LEEM). Since then several other surface imaging methods with slow electrons have emerged, in particular synchrotron radiation excited photo emission electron microscopy (XPEEM). In LEEM the high intensity of the diffracted slow electrons allows fast image acquisition. Therefore it is tempting to combine it with the other, slower complementary methods. This has been accomplished in the Spectroscopic Photo Emission and Low Energy Electron Microscope (SPELEEM) by adding an energy filter. Today the SPELEEM allows comprehensive structural, chemical, magnetic, electronic characterization of surfaces and thin films by imaging with 10 nm lateral resolution and atomic depth resolution, diffraction and spectroscopy. Recent developments are expected to push the resolution limit into the 1 nm range by aberration correction and the time resolution into and below the picosecond range by pulsed illumination and time-delayed triggered detection. The talk will first describe the general imaging principles and then illustrate with a number of examples the possibilities and limitations of some of the methods, LEEM, Spin-Polarized LEEM (SPLEEM) and X- ray Magnetic Dichroism PEEM (XMCDPEEM). A brief outlook will conclude the presentation. [Preview Abstract] |
Monday, March 21, 2005 1:03PM - 1:39PM |
B3.00004: David Adler Lectureship Award Talk: Multifunctional Complex Oxide Heterostructures Invited Speaker: Complex perovskite oxides exhibit a rich spectrum of functional responses, including magnetism, ferroelectricity, highly correlated electron behavior, superconductivity, etc. There exists a small set of materials which exhibit multiple order parameters; these are known as multiferroics. Using our work in the field of ferroelectrics and magnetoresistice oxides (CMR) as the background, we are now exploring such materials, as epitaxial thin films as well as nanocomposites. Specifically, we are studying the role of thin film growth, heteroepitaxy and processing on the magnitude of the coupling between the order parameters. In single phase multiferroic perovskites, such as BiFeO3, we have found enhancements in magnetism and ferroelectricity compared to bulk. Detailed measurements indicate the possibility that the enhancement in magnetism is due to a mixed Fe+2/Fe+3 state in the films. A very exciting new development has been the discovery of the formation of spontaneously assembled nanostructures consisting of a ferromagnetic phase embedded in a ferroelectric matrix that exhibit very strong coupling between the two order parameters. This involves 3-dimensional heteroepitaxy between the substrate, the matrix perovskite phase and spinel phase that is embedded as single crystalline pillars in this matrix. This epitaxial coupling is critical and is responsible for the significantly higher magnetoelectric coupling and magnetic anisotropy in such vertical heterostructures compared to a conventional heterostructure. This work is supported by the UMD-MRSEC and by the ONR under a MURI program. [Preview Abstract] |
Monday, March 21, 2005 1:39PM - 2:15PM |
B3.00005: McGroddy Prize Talk: Competing orders and gigantic responses in transition-metal oxides with correlated electrons Invited Speaker: Transition-metal oxides offer an intriguing playground to find amazing electronic property/functionality, such as high-temperature superconductivity in copper-oxides and colossal magnetoresistance in manganese-oxides. In those materials, a vast number of electrons, comparable to the number of the constituent atoms, are strongly interacting with each other and tend to lose their mobility. These correlated electrons with internal degrees of freedom- charge, spin, and orbital-, when placed on the specific topological atomic lattice, may form the rich and complex phases or the self-organized structures. Those are, for example, charge- spin stripes, charge-orbital ordered states, and liquid-crystal like states with anisotropic charge-spin-orbital correlations. Here I would present some of ample examples of the correlated-electron's ordering patterns and show how dramatically they can respond to external stimuli, say, electric/magnetic fields, light, and pressure. In particular, the response of correlated electrons can be huge and fast in the vicinity of the boundary of the competing electronic phases, which promises future application. [Preview Abstract] |
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