Physics Colloquium

Spring 2011

Thursdays 4:00 p.m., Room 104 Physics
Refreshments served at 3:40 p.m.
  Colloquium organizer: Alexey Yamilov
(Link to main colloquium page)

Green - open date
Yellow - tentative (reserved)
Red - firm commitment

January
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Date Host Speaker Title of the talk Abstract
Jan. 20



Jan. 27 Yamilov
Kai Song
S&T's MRC
Electron Microscopy in Materials Science – Case studies in superalloy, Fe-zeolite catalyst, metal/ceramic thin film on glass and yttrium-doped ceramics Scanning/Transmission Electron Microscope (S/TEM) is the most powerful analytical tool in the field of Materials Science and has found widespread application across the scientific disciplines. Recently, with the advance of field-emission gun and aberration-correcting techniques, the state-of-the-art S/TEM can resolve structure details of crystalline materials at sub-nanometer scale (where 1 nm = 10-9 m) or atomic resolution. This makes S/TEM an indispensable tool for understanding structural and chemical information of nanostructured materials.
   This talk briefly explores the mechanism for imaging and composition analysis in S/TEM. Then several case studies are presented regarding utilization of S/TEM in microstructural characterization of engineering materials, including Fe-zeolite catalyst, metal/ceramic thin film on glass and yttrium-doped silicon nitride. These studies utilized a number of analytical techniques such as Diffraction, High Resolution Lattice Imaging, High-Angle Annual Dark Field imaging (HAADF), X-ray Energy Dispersive Spectrometry (EDX), Electron Energy Loss Spectroscopy (EELS) and Energy-Filtered TEM (EFTEM). Applicability of the individual techniques to determine structural/chemical information at nanometer scale is highlighted.
Feb. 3 Jentschura Charles Munger, Jr.
SLAC
Electric dipole moments of fundamental particles The Standard Model predicts the existence of electric dipole moments of fundamental particles that are many orders of magnitude below existing experimental upper limits.  Other models predict that such moments are generically much larger, and these models can be severely constrained if the upper limit is lowered, or confirmed if a finite moment is found. Advances in trapping and cooling atoms and in state preparation, it is argued, make possible lowering the upper limit on the electron electric dipole moment by two orders of magnitude (to 10^{-50} Coulomb * Meter) by using a cesium atomic fountain. Though new sources of systematic error become important at this level of sensitivity, schemes of canceling most such errors and of limiting and bounding the rest make such an experiment feasible.
Feb. 10 Medvedeva Joseph Heremans
Ohio State
High-efficiency thermoelectric materials: new design strategies, new applications Thermoelectric energy converters are solid state devices that convert thermal to electrical energy, and are used in heat pumps and power generators.  They have no moving parts, conveying them the inherent advantages of compactness and robustness that have traditionally been offset by their low efficiency.  This changed in the last decade when several classes of materials were developed with double the efficiency of commercial materials.  Consequently, the new materials are poised to play a significant role in energy recovery applications from waste heat, and in new efficient air-conditioning schemes.
   This talk will briefly review the new applications, as well as the recent materials design strategies used.  Almost all the progress to date has come from reductions in thermal conductivity obtained using nanotechnologies or structural disorder.  In 2008, we developed a new strategy based on resonant impurity doping, which doubled the efficiency of p-type PbTe, the semiconductor used in power generation around 500oC.  We recently extended this approach to Bi2Te3, which is used in Peltier coolers.  The physical mechanism underlying this improvement was originally developed for metals by Korringa, and later Friedel, and is similar to the Kondo effect in dilute magnetic alloys.
Feb. 17 Yamilov Kartik Ghosh
Missouri State
Nanoscale Investigation of Domain Dynamics in Multiferroic Thin Films using Scanning Probe Microscope Recently, simultaneous ferromagnetic and ferroelectric orderings have been observed in a single phase perovskite oxides as well as nanocomposite materials with perovskite oxides. These materials are called multiferroics. It has also been found that in some multiferroic materials ferroelectric and magnetic orderings not only coexist in the same material but also couple strongly that the magnetic degree of freedom can be manipulated by an electric field and the electric degree of freedom can be manipulated by a magnetic field. These unique properties promise potential multifunctional devices such as tunnel magneto resistance (TMR) sensors, non-volatile ferroelectric random access memories, and tunable microwave devices. The magnetoelectric effects depend on the microscopic domain structure of multiferroics. Thus direct imaging of domain structures and investigation of their behavior under both electric and magnetic field can provide a microscopic origin of switching phenomena and the role domains play in magnetoelectric effect in multiferroics.  Scanning probe microscopy (SPM) is a useful technique for investigation of multiferroic materials, providing high-resolution visualization of ferroelectric as well as ferromagnetic domains. This talk will explain how a SPM can be used to read, write, and erase data in both ferroelectric and ferromagnetic materials. Also I will discuss how SPM can be used to investigate magnetoelectric coupling in multiferroics. A better understanding of the multiferroics will lead us to make advanced logic and memory devices and tunable microwave filters that can be used in many electronic devices such as computers, digital cameras, and cell phones.
Feb. 24 Jentschura Stan Brodsky
SLAC
Novel Aspects of Hadron Physics Quantum Chromodynamics provides a fundamental description of hadron and nuclear physics in terms of permanently confined quark and gluon constituents.
   QCD has many remarkable and novel features, such as color transparency, hidden color, intrinsic charm, direct hard subprocesses, in-hadron condensates, as well as unexpected non-factorizing phenomena due to to initial and final-state interactions.
   I  will also discuss new insights into QCD that have recently been obtained from theories in higher-space time dimensions and a new theoretical tool,  light-front holography. 
Mar. 3 Yamilov Guoqiang Li
UMSL
Adaptive lens for vision correction and biomedical imaging Recent advances in adaptive lenses are reviewed with a focus on applications in vision care and biomedical imaging. The electro-optic lens allows voltage controlled change of the focusing power across the entire aperture. Such a lens must have high light efficiency, relatively large aperture, fast switching time, low driving voltage, and power-failure-safe configuration. Adaptive liquid crystal lenses and liquid lenses that satisfy these requirements will be presented. The adaptive lenses provide the capability of corrections for near-, intermediate-, and distance-vision for presbyopic eyes and lenses with large tunable range may be used as a phoropter. They may have revolutionary impact on the field of vision care. Other applications of adaptive lenses in depth-resolved biomedical optical imaging will be discussed.
Mar. 17 Vojta JosÚ Abel Hoyos
University of Sao Paulo
Randomness in one dimensional quantum systems We overview the effects of quenched disorder in a variety of quantum
critical 1D systems: the Ising and Heisenberg models and their variations. In all cases studied, it is possible to classify all universality classes according to the strength of the effective randomness in the low-temperature limit using a single analytical method. We give further simple symmetry-based arguments in order to understand these universality classes and discuss the implications of our results on quantum phase transitions.
Mar. 24 Yamilov Lifeng Dong
Missouri State
Electron Microscopy Observations of Carbon Nanomaterials
Electron microscopy and microanalysis can be used to explore correlations between morphology, structures, and compositions of various materials and their electrical, optical, magnetic, and biological properties. Several types of carbon nanomaterials with different chemical and physical properties, such as fullerene C60, carbon nanotubes, graphene, and carbon nanofibers, have been synthesized and extensively investigated for potential applications in electronics, optoelectronics, solar cells, fuel cells, and biomedicine. In this talk, aberration-corrected transmission electron microscopy equipped with electron energy loss spectroscopy was employed to explore the hybrids of carbon nanotubes and DNA molecules and their delivery into cells, DNA-templated synthesis of platinum nanoparticles on carbon nanotubes and their electrocatalytic activity for methanol oxidation, as well as the migration of copper catalysts inside helical carbon nanofibers.
Apr. 7 Schulz Klaus Bartschat
Drake University
Single and Double Ionization of Atoms and Molecules
by Short-Pulse Intense Laser Fields and Charged-Particle Impact
The yield and the angular distribution of ejected electrons in strong-field ionization can be strongly dependent on the intensity, length, and carrier envelope of the incident laser radiation.  We investigate these effects by solving the time-dependent Schr÷dinger equation directly on a numerical space-time grid.  Many methods have been suggested to achieve this goal.  We discuss how their effectiveness and appropriateness usually depend on the details of the problem at hand.  Results will be presented for single ionization of hydrogen, helium, and heavy noble gases, as well as for double ionization of helium and molecular hydrogen.  We also illustrate how the use of two pulses with a fixed delay can yield additional information in so-called "pump-probe" setups.  Finally, the connection to the treatment of heavy-particle impact in a time-dependent framework will be discussed.
Apr. 14 Medvedeva Evgeny Tsymbal
University of Nebraska-Lincoln
Ferroelectric Tunnel Junctions:
Controlling Electron and Spin Transport by Ferroelectric Polarization
Tunnel junctions are useful electronic devices in which current-carrying electrons can quantum-mechanically be transmitted between two metal electrodes across a very thin insulating barrier layer. A particular example is a magnetic tunnel junction, where electrical resistance depends on magnetization orientation of the two ferromagnetic electrodes – the phenomenon known as tunneling magnetoresistance (TMR). So far, however, almost all the existing tunnel junctions were based on non-polar dielectrics. An exciting possibility to extend the functionality of tunnel junctions is to use a ferroelectric insulator as a barrier to create a ferroelectric tunnel junction (FTJ). [1] The key property of FTJ is tunneling electroresistance (TER) that is the change in electrical resistance of a FTJ with reversal of ferroelectric polarization. Functional properties of a FTJ can be further extended by ferromagnetic electrodes to create a multiferroic tunnel junction (MFTJ).  In such a MFTJ the transport spin polarization and TMR are affected by ferroelectric polarization of the barrier. [E. Y. Tsymbal and H. Kohlstedt, Science 313, 181 (2006)] Thus, MFTJs represent four-state resistance devices that can be controlled both by electric and magnetic fields. This talk will address the physics of FTJs and MFTJs based on recent modeling and experiments.  
Apr. 21 Yamilov R. Mark Wagner
Large Binocular Telescope Observatory
The Large Binocular Telescope:
Seeing the Universe in a New Light
The Large Binocular Telescope Observatory is located in southeastern Arizona at an altitude of 3191 m (10470 feet). The binocular design of the Large Binocular Telescope (LBT) has two identical 8.4 m diameter telescopes mounted side-by-side on a common altitude-azimuth mounting for a combined collecting area of a single 11.8 m telescope. The two primary mirrors are separated by 14.4 m and provide an interferometric baseline of almost 23 m. The binocular design, combined with integrated adaptive optics utilizing adaptive Gregorian secondary mirrors and ultimately a laser guide star system to compensate for atmospheric phase errors, provides a large effective aperture, high angular resolution, low thermal background, and exceptional sensitivity for the detection of faint objects. The LBT is an international collaboration of the University of Arizona, Italy (INAF: Istituto Nazionale di Astrofisica), Germany (LBTB: LBT Beteiligungsgesellschaft), The Ohio State University, and the Tucson-based Research Corporation. We will summarize status of the LBT and its context with respect to current and planned facilities, its scientific instruments and their capabilities, as well as present some recent scientific results.
Apr. 28 Yamilov 40th Annual Harold Q. Fuller Prize Colloquium

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