Skip to content
University of Maryland LibrariesDigital Repository at the University of Maryland
    • Login
    View Item 
    •   DRUM
    • Theses and Dissertations from UMD
    • UMD Theses and Dissertations
    • View Item
    •   DRUM
    • Theses and Dissertations from UMD
    • UMD Theses and Dissertations
    • View Item
    JavaScript is disabled for your browser. Some features of this site may not work without it.

    Optical Properties of Strongly Correlated Transition Metal Oxides

    Thumbnail
    View/Open
    umi-umd-2046.pdf (26.16Mb)
    No. of downloads: 2032

    Date
    2004-12-14
    Author
    Simpson, Jeffrey Ray
    Advisor
    Drew, Howard D.
    Metadata
    Show full item record
    Abstract
    The strong electron interactions in transition metal oxides offer wide-ranging phenomena of interest to condensed matter physics and potential applications in novel electronic devices. This thesis focuses on optical studies performed on three such systems: colossal magnetoresistant (CMR) manganites, multiferroic LuMnO<sub>3</sub>, and dilute magnetic oxide (DMO) cobalt-doped TiO<sub>2</sub>. Optical measurements, using a variety of techniques, of thin film and bulk samples extend over a range of frequencies (0.002-5 eV) and temperatures (4-350 K) and determine the optical constants. Optical properties provide important insights into the electronic structure of these exciting systems and illustrate the value of optical measurements as a probe of novel materials. The pseudocubic manganites exhibit a rich phase diagram that includes, in addition to CMR, various types of magnetic, charge, and orbitally ordered phases. For the CMR manganites, the optical spectra and oscillator strength changes compare with models that require both double exchange and the dynamic Jahn-Teller effect in the description of the electronic structure. In the ferromagnetic state, results on the electronic scattering rate and mass enhancement refute the claims of an anomalously small Drude weight in these materials. Smaller rare-earth ions in the manganites (<i>e.g.</i>, Lu) result in crystallization into a hexagonal structure and a multiferroic ground state, in which ferroelectricity and antiferromagnetism occur simultaneously. A symmetry-allowed on-site Mn <i>d-d</i> optical transition blueshifts in the antiferromagnetic state resulting from Mn-Mn superexchange. TO phonon frequencies exhibit similar temperature dependent shifts arising from spin-phonon interactions. Further, these phonons dominantly contribute to the known anomaly below <i>T<sub>N</sub></i> of the quasi-static dielectric constant. Cobalt-doped TiO<sub>2</sub> has received recent attention as a new DMO displaying room temperature ferromagnetism. Optical conductivity of low-doped samples reveals an absence of absorption below an onset of interband transitions at 3.6 eV and a blue shift of the band edge with doping. The absence of below band gap absorption remains inconsistent with band calculations and suggests that strong on-site Coulomb interactions shift the optical transitions to energies above the gap.
    URI
    http://hdl.handle.net/1903/2079
    Collections
    • Physics Theses and Dissertations
    • UMD Theses and Dissertations

    DRUM is brought to you by the University of Maryland Libraries
    University of Maryland, College Park, MD 20742-7011 (301)314-1328.
    Please send us your comments.
    Web Accessibility
     

     

    Browse

    All of DRUMCommunities & CollectionsBy Issue DateAuthorsTitlesSubjectsThis CollectionBy Issue DateAuthorsTitlesSubjects

    My Account

    LoginRegister
    Pages
    About DRUMAbout Download Statistics

    DRUM is brought to you by the University of Maryland Libraries
    University of Maryland, College Park, MD 20742-7011 (301)314-1328.
    Please send us your comments.
    Web Accessibility