Physics Colloquium

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The Physics of Biomolecules Presenter(s): The University of Tennessee Type: On Demand Air Date: 11/30/2009 Air Time: 3:30 PM EST Duration: 1 Hour 10 Minutes 59 Seconds Physics Colloquium Monday, November 30, 2009 Jeremy Smith UT-ORNL Governor’s Chair “The physics of biomolecules” Talk: 3:30 p.m. , Room 307 SERF Refreshments: 3:00 p.m.	STAR and ALICE Physics Presenter(s): The University of Tennessee Type: On Demand Air Date: 11/23/2009 Air Time: 3:30 PM EST Duration: 1 Hour 12 Minutes 9 Seconds John Harris, Yale University
High Temperature Superconductors Presenter(s): The University of Tennessee Type: On Demand Air Date: 11/16/2009 Air Time: 3:30 PM EST Duration: 1 Hour 4 Minutes 23 Seconds	Direct Searches for Dark Matter Particles Presenter(s): The University of Tennessee Type: On Demand Air Date: 11/9/2009 Air Time: 3:30 PM EST Duration: 1 Hour 11 Minutes 29 Seconds Dan McKinsey, Yale University "Direct searches for dark matter particles" Astrophysical evidence on a variety of distance scales clearly shows that we cannot account for a large fraction of the mass of the universe. This matter is “dark,” not emitting or absorbing any electromagnetic radiation. A compelling explanation for this missing mass is the existence of Weakly Interacting Massive Particles (WIMPs). These particles are well motivated by particle physics theories beyond the Standard Model, and the discovery of WIMPs would have enormous impact on both astrophysics and particle physics. WIMPs, if they exist, would occasionally interact with normal matter. With a mass in the range of 1 to 1000 times the mass of the proton, and moving at speeds relative to the Earth of about 220 km/s (the velocity of the Sun around the MilkyWay), WIMPs would only deposit a small amount of energy when scattering with nuclei. Detectors that are low in radioactivity and sensitive to small energy depositions can search for the rare nuclear recoil events predicted by WIMP models. One experiment, known as DAMA, claims a dark matter signal based on an observed annual modulation of the event rate in sodium iodide crystals. In recent years, several new efforts on direct dark matter detection have begun in which the detection material is a noble liquid. Advantages include: large nuclear recoil signals in both scintillation and ionization channels, good scalability to large target masses, effective discrimination against gamma ray backgrounds, easy purification, and reasonable cost. Talk: 3:30 p.m.; 307 SERF Refreshment: 3:00 p.m.
Merging Black Holes Presenter(s): The University of Tennessee Type: On Demand Air Date: 11/2/2009 Air Time: 3:30 PM EST Duration: 1 Hour 9 Minutes 56 Seconds Joan Centrella, NASA Goddard Space Flight Center "Merging black holes" The final merger of two black holes is expected to be the strongest source of gravitational waves for both ground-based detectors such as LIGO and VIRGO, as well as the space-based LISA. Since the merger takes place in the regime of strong dynamical gravity, computing the resulting gravitational waveforms requires solving the full Einstein equations of general relativity on a computer. For many years, numerical codes designed to simulate black hole mergers were plagued by a host of instabilities. However, recent breakthroughs have conquered these instabilities and opened up this field dramatically. This talk will focus on the resulting gold rush of new results that are revealing the dynamics and waveforms of binary black hole mergers, and their applications in gravitational wave detection, testing general relativity, and astrophysics. November 2, 2009 Talk: 3:30 p.m.; Room 307 SERF Refreshment: 3:00 p.m.	Feng Chen Presentation - October 26th, 2009 Presenter(s): The University of Tennessee Type: On Demand Air Date: 10/26/2009 Air Time: 3:30 PM EDT Duration: 1 Hour 12 Minutes 9 Seconds
The Puzzle of Charge and Mass Presenter(s): The University of Tennessee Type: On Demand Air Date: 10/26/2009 Air Time: 3:30 PM EDT Duration: 1 Hour 15 Minutes 9 Seconds Stuart Raby, The Ohio State University Title: "The Puzzle of Charge and Mass" Beginning with the seminal work of Rutherford, Geiger and Marsden in 1911, physicists have investigated the atom using particle beams (alpha particles, and protons) as probes. They developed new detection methods; the geiger counter, scintillators, cloud and then bubble chambers. This new paradigm for probing matter and new detectors led to many discoveries. To make a long story short, by 1974 the chaos of discovery lead to the Standard Model describing all observed particle phenomena in terms of three fundamental forces (4 including gravity) and the fundamental building blocks of matter, quarks and leptons. Only now, after the dust of this chaotic discovery settles, are we able with hindsight to recognize the underlying principles which define the theory we call the Standard Model. It is these principles and their logical extension which I will attempt to describe in this talk. Talk: 3:30 p.m. in room 307 SERF Refreshments: 3:00 p.m.	Glass Transition and its Relevance to Biological Systems Presenter(s): The University of Tennessee Type: On Demand Air Date: 10/12/2009 Air Time: 3:30 PM EDT Duration: 1 Hour 5 Minutes 20 Seconds Alexei P. Sokolov UT/ORNL Governor’s Chair For thousands of years people are using glass transition process and glasses in their everyday life. For hundreds of years researchers are studying the glass transition phenomenon. However, understanding the microscopic mechanism underlying the tremendous slowing down of structural relaxation remains one of the main challenges in current condensed matter physics. This talk will present an overview of new ideas and experimental results generated in this field during the last two decades. It appears that the glass transition on a molecular level occurs at temperatures much above the conventional glass transition temperature. Understanding of this important point shifted significantly the focus of the current research and resulted in deeper microscopic understanding of the glass transition. In a recent decade it has been realized that the glass transition is actively used in nature. In particular, living organisms use the glass transition to survive in extreme environmental conditions. A role of the glass transition in biology and in preservation of biological molecules and organisms will be discussed at the end of the talk. Physics Colloquium October 12, 2009 Room: 307 SERF; Talk: 3:30 p.m. Refreshments: 3:00 p.m.
Frustrated and Satisfied Ground States in Pyrochlore Magnets Presenter(s): The University of Tennessee Type: On Demand Air Date: 9/28/2009 Air Time: 3:30 PM EDT Duration: 1 Hour 10 Minutes 30 Seconds Bruce Gaulin, McMaster University "Frustrated and Satisfied Ground States in Pyrochlore Magnets" Geometrical frustration arises quite generally when pairwise interactions in magnetic materials are incompatable with their local geometry. This often involves magnetic materials made up of assemblies of triangles or tetrahedra. The frustration is manifest by disordered low temperature states for the magnetic material - some of which are described by spin liquids, spin glasses, and spin ice. I will discuss (mostly) neutron scattering work on two magnetic pyrochlores Tb2Ti2O7 and Ho2Ti2O7, which can be thought of as Ising-like moments decorating a network of corner-sharing tetrahedra. Tb2Ti2O7 displays a spin liquid, or cooperative paramagnetic ground state, but can be brought to order in an applied magnetic field. Ho2Ti2O7 displays a static disordered "spin ice" state at low temperatures Talk: 3:30 p.m.; 307 SERF Refreshment: 3:00 p.m.	Planets Around Evolved Stars Presenter(s): The University of Tennessee Type: On Demand Air Date: 9/21/2009 Air Time: 3:30 PM EDT Duration: 1 Hour 6 Minutes 40 Seconds Alex Wolszczan, Penn State University Center for Exoplanets and Habitable Worlds "Planets around evolved stars" Discoveries of planets around Sun-like stars have taught us much about the nature of extrasolar planetary systems. However, issues such as planet formation around higher mass stars and long-term evolution of planetary systems have been left out from the mainstream exoplanet research, because the radial velocity method of planet detection becomes inefficient for spectral types earlier than F6-F8. An attractive way to remove this deficiency is to search for planets around giant stars, which have cool atmospheres and their spectra are rich in absorption lines that can be used for planet detection. In addition, planets have been discovered around neutron stars, a post-red-giant star and, possibly, around at least one white dwarf, all of which demonstrates the spectacular robustness of the planet formation process. In this talk, I will review the development of this relatively new field in the exoplanet research and present the Penn State - Torun Centre for Astronomy search for planets around GK-giants and other stars with the 9.2-m Hobby-Eberly Telescope. Talk at 3:30 p.m.; 307 SERF Refreshments: 3:00 p.m.
TRIUMF, Canada's National Laboratory for Particle and Nuclear Physics Presenter(s): The University of Tennessee Type: On Demand Air Date: 9/14/2009 Air Time: 3:30 PM EDT Duration: 1 Hour 7 Minutes 49 Seconds Achim Schwenk, TRIUMF, Canada's National Laboratory for Particle and Nuclear Physics "A tour of neutron-rich matter in the universe" I will take you on a tour of the physics of neutrons in the universe. The tour leads us through astrophysics, atomic, nuclear and particle physics and highlights: § the physics of strong interactions between neutrons, § universal properties of neutrons and ultracold atoms, § neutron superfluidity in neutron stars, § novel forms of matter and the limits of existence of neutron-rich nuclei, and § how neutrinos interact with neutrons in supernovae. Talk: 3:30 p.m. at 307 SERF Refreshment: 3:00 p.m.	Mathematical Challenges in Theoretical Biology: Networks, Dynamics, and Noise Presenter(s): The University of Tennessee Type: On Demand Air Date: 8/31/2009 Air Time: 3:30 PM EDT Duration: 1 Hour 9 Minutes 30 Seconds Jaewook Joo, UT Physics/NIMBioS "Mathematical challenges in theoretical biology: networks, dynamics, and noise" A key aim of postgenomic biomedical research is to systematically understand the structure and the dynamics of the complex intercellular web of interactions between proteins, DNA, RNA, and small molecules that contribute to the function of a living cell. Such a network of interactions is a dynamic system evolving in time and space according to fundamental laws of reaction, diffusion and transport. These laws govern how a biological network, confronted by any set of stimuli, determines the appropriate response of a cell. This information processing system can be described in precise mathematical terms and the resulting equations can be analyzed and simulated to provide reliable, testable accounts of the molecular control of cell behavior. In this talk, I will discuss the mathematical challenges in understanding the dynamics of the complex biological networks and especially will focus on the effect of noise on such a dynamical system. Talk at 3:30 p.m. Place; 307 SERF Refreshment: 3:00 p.m.
Physics - August 24, 2009 Presenter(s): The University of Tennessee Type: On Demand Air Date: 8/24/2009 Air Time: 3:31 PM EDT Duration: 1 Hour 11 Minutes 3 Seconds	Honor's Presentation 2009 Presenter(s): The University of Tennessee Type: On Demand Air Date: 4/20/2009 Air Time: 3:30 PM EDT Duration: 1 Hour 6 Minutes 14 Seconds
Dark Energy: the Cosmological Constant in Disguise Presenter(s): The University of Tennessee Type: On Demand Air Date: 4/13/2009 Air Time: 3:30 PM EDT Duration: 1 Hour 9 Minutes 19 Seconds Physics Colloquium: Monday, April 13 Stephon Alexander, Department of Physics and Astronomy, The Koshland Center for Integrated Sciences Haverford College "Dark Energy: the Cosmological Constant in Disguise" Recent cosmological observations have reached the conclusion that our universe undergoing an accelerated expansion. A mysterious unknown substance called Dark Energy is needed to drive this acceleration. This dark energy resurrects the infamous cosmological constant problem back into theoretical physics. Moreover, the best paradigm which solves the problems of the standard big bang cosmology is an early phase of rapid acceleration (cosmic inflation), requiring a much larger value of the same dark energy substance. The existence and nature of dark energy has surprised and mystified cosmologists. In this colloquium I will review cosmic inflation and the dark energy/cosmological problem and discus the challenges that they bring to theoretical physics. Finally, I will provide a novel mechanism which potentially connects dark energy to neutrino vacuum oscillations.	A New Piece in the High Tc Superconductivity Puzzle: Fe Based Superconductors Presenter(s): The University of Tennessee Type: On Demand Air Date: 4/6/2009 Air Time: 3:30 PM EDT Duration: 1 Hour 14 Seconds An overview of the historic and current developments in superconductivity will be be presented. The phenomenon of superconductivity was discovered almost 100 hundred years ago and it is still one of the hottest research topics providing fascinating puzzles and challenges to both theoreticians and experimentalists. There was a lag of almost 50 years between the experimental discovery of (low Tc) superconductivity and the development of the BCS theory which explained the phenomenon in terms of pairs of electrons held together by the phonons in the material. The quest to discover superconducting materials with higher Tc's continued quietly for many years until huge progress occurred twenty years ago when Tc's higher than 77K were observed in copper-oxide based materials. The study of these new materials generated tremendous advances in both experimental and theoretical methods and much is now known about their properties, but the mechanism, i.e., the ``glue'', that binds the electrons together is still unknown; it appears that phonons are unable to do the job and there is controversy on whether the magnetism present in these materials helps or hurts. Just one year ago high Tc was discovered in a new family of iron based materials. While they are similar to the cuprates in some ways, i.e., magnetism is present, there are many differences as well. This discovery provides a new chance to unveil the high-Tc mystery and the condensed matter community is intensely working on the subject. Talk at 3:30 p.m. in 307 SERF
Berry Phase: The Missing Ingredient in the Electron Theory of Materials Presenter(s): The University of Tennessee Type: On Demand Air Date: 3/9/2009 Air Time: 3:30 PM EDT Duration: 1 Hour 4 Minutes 35 Seconds Di Xiao Materials Science & Technology Division Oak Ridge National Laboratory Berry phase: The missing ingredient in the electron theory of materials The theory of band structure in crystalline solids provides the fundamental basis for understanding materials and phenomena. It is generally believed that for most physical applications the energy dispersion alone carries sufficient information to give proper account of various thermodynamic and transport properties. Recently, this belief is challenged by the realization that the Berry phase of the electronic wave function can also have a profound effect on materials properties and is responsible for a spectrum of phenomena, such as the quantum/anomalous/spin Hall effects and ferroelectricity. In my talk, I will show that the Berry phase effects can be systematically studied through its modification to the electron dynamics and the density of states. The important consequence of this modification is demonstrated by several examples, including valley Hall effect in graphene, orbital magnetization, and ferroelectricity in inhomogeneous materials such as multiferroics. Given its broad range of applications and essential role in understanding these phenomena, it is clear that the Berry phase should be included as a basic ingredient in the electron theory of materials. Physics Colloquium, Monday, March 9, 2009 Talk: 3:00 p.m. in room SERF 307 Refreshments: 3:00 p.m.	Bright Lights, Dark Energy, and a Quite Curious Coefficient: Thermonuclear Supernovae and the Equation of State for the Universe Presenter(s): The University of Tennessee Type: On Demand Air Date: 3/2/2009 Air Time: 3:30 PM EST Duration: 1 Hour 9 Minutes 10 Seconds Mike Guidry Department of Physics and Astronomy University of Tennessee Physics Division Oak Ridge National Laboratory An equation of state is a relationship among thermodynamic variables that typically goes beyond the information supplied by thermodynamics alone. What then is the equation of state for the Universe as a whole? We believe that this most profound of questions has a conceptually simple answer: the pressure of the Universe is proportional to its energy density. Causality arguments require that the coefficient of proportionality be less than or equal to 1, but it is only within the past decade that observations have begun to close in on the actual value of this elusive coefficient. These observations indicate that the Universe is permeated by a mysterious "dark energy" causing the expansion of the Universe to accelerate. This requires the coefficient to have a value less than -1/3 (which is most curious, since this means that the Universe on large scales has an equation of state fundamentally different from any ever measured in a local laboratory within that Universe!). To constrain it further requires parallel improvements in observational technology and the theoretical understanding of those observations. The key tool is comparison of observed brightness with expected brightness for some of the most luminous objects in the sky, Type Ia (thermonuclear) supernovae. I will provide an overview of these issues that is accessible to non-astronomers, and describe our own efforts to contribute through a more fundamental understanding of the Type Ia mechanism.
The Story Your Proteins Could Tell: Evolution of a Complex Biological System Presenter(s): The University of Tennessee Type: On Demand Air Date: 2/23/2009 Air Time: 2:12 PM EST Duration: 1 Hour 10 Minutes 53 Seconds Igor B. Jouline (Zhulin), Joint Faculty Professor and Distinguished R&D Staff Member National Institute for Computational Sciences (UT/ORNL) "The Story Your Proteins Could Tell: Evolution of a Complex Biological System" You've heard about atoms. Now it's time for complex molecules. One of the "debatable" questions in the evolution of Life on Earth is the issue of complexity. For instance, Intelligent Design is based on the notion of irreducible complexity: biological systems are so complex that they cannot be effectively reduced to simple components. We use a computational genomic approach to demonstrate that evolution of a complex system that regulates behavior of living organisms can be effectively traced from simplest proteins to multi-protein machinery as a chain of incremental innovations followed by diversification. What's in there for a physicist? Well, just a chance to forget about physics for a moment and to learn about another "stamp collection" (according to Ernest Rutherford).	The Story Your Atoms Could Tell Presenter(s): The University of Tennessee Type: On Demand Air Date: 2/16/2009 Air Time: 3:30 PM EST Duration: 1 Hour 8 Minutes 36 Seconds Raph Hix, ORNL/UT The atoms that make up our bodies and our world were made over the billions of years of cosmic history. The story of their creation links us to some of the most spectacular events in the universe. We will discuss some of the astrophysical actors that play a role in this story and the ongoing work of UTK/ORNL Theoretical Astrophysics group to help refine our understanding of our origins.
Status and Progress at the Sanford Lab at Homestake Presenter(s): The University of Tennessee Type: On Demand Air Date: 2/9/2009 Air Time: 3:30 PM EST Duration: 1 Hour 10 Minutes 48 Seconds Jose Alonso, Sanford Underground Laboratory at Homestake In July 2007, the Homestake gold mine in the Black Hills of South Dakota was selected by the NSF as the site for DUSEL (the Deep Underground Science and Engineering Laboratory). The SDSTA (South Dakota Science and Technology Authority), landlord of the mine property and charged by the State to re-open the mine, has undertaken the process of refurbishing shafts, re-establishing water-pumping infrastructure and deploying of an “early science” program, all in preparation for the formal commencement of DUSEL construction anticipated in FY13. Excellent progress on all these fronts is being made, and will be reported. Water level is dropping steadily as we pump and treat approximately 2 million gallons of water per day; we expect to have the 4850 level dry in a few months. Early science includes LUX (liquid-xenon dark-matter search), elements of the Majorana (0ν β β) experiment, and deployment of several seismometer stations. A first micro-biology paper has just been published!	Between electronics and Photonics: Terahertz Investigations of Complex Condensed Matter Presenter(s): The University of Tennessee Type: On Demand Air Date: 1/12/2009 Air Time: 3:30 PM EST Duration: 1 Hour 2 Minutes 48 Seconds Physics Colloquium Monday, January 12, 2009 Peter Armitage John Hopkins University
"Toward a Dark Matter Telescope" Presenter(s): The University of Tennessee Type: On Demand Air Date: 11/24/2008 Air Time: 3:30 PM EST Duration: 48 Minutes 30 Seconds November 24th, 2008 - Denis Dujmic, Massachusetts Institute of Technology	The Entanglement Your Mother Never Warned You About Presenter(s): The University of Tennessee Type: On Demand Air Date: 11/17/2008 Air Time: 3:30 PM EST Duration: 1 Hour 4 Minutes 5 Seconds November 17th, 2008 - Warren Grice, Oak Ridge National Lab
Insights in High-TC Superconductivity from Atomic-layer Engineering Presenter(s): The University of Tennessee Type: On Demand Air Date: 11/10/2008 Air Time: 3:30 PM EST Duration: 1 Hour 17 Minutes 25 Seconds November 10th, 2008 - Ivan Bozovic, Brookhaven National Laboratory	Science of Rare Isotopes: Connecting Nuclei with the Universe Presenter(s): The University of Tennessee Type: On Demand Air Date: 11/3/2008 Air Time: 3:30 PM EST Duration: 1 Hour 3 Minutes 27 Seconds November 3rd, 2008 - Witek Nazarewicz, UT/ORNL
Transport Processes in Dilute Plasmas Presenter(s): The University of Tennessee Type: On Demand Air Date: 10/27/2008 Air Time: 3:30 PM EDT Duration: 1 Hour 14 Minutes 50 Seconds October 27th, 2008 - Leopolda Garcia-Colin, Universidad Autonoma Metropolitana-Iztapalapa in Mexico	Atomic Interferometry for Detection of Gravity Waves Presenter(s): The University of Tennessee Type: On Demand Air Date: 10/20/2008 Air Time: 3:30 PM EDT Duration: 59 Minutes 48 Seconds October 20th, 2008 - Mark Kasevich, Stanford University
Frontiers of the Nuclear Quantum Many-Body Problem Presenter(s): The University of Tennessee Type: On Demand Air Date: 10/13/2008 Air Time: 3:30 PM EDT Duration: 12 Minutes 59 Seconds October 13th, 2008 - Thomas Papenbrock, University of Tennessee	Applying Nuclear Physics to Address Challenges in National Security Presenter(s): The University of Tennessee Type: On Demand Air Date: 10/6/2008 Air Time: 3:30 PM EDT Duration: 1 Hour 3 Minutes 2 Seconds October 6th, 2008 - Jolie Cizewski, Rutgers University Should the unthinkable occur and a nuclear device is exploded by a terrorist group or rogue nation, nuclear forensics can be applied to help identify the source of the material. In nuclear forensics, the recovered material is compared with information in databases or expectations from models of nuclear devices. To provide the base line data to help identify the source and composition of the nuclear material, there is a need to understand better the nuclear reaction processes that could occur. A particular challenge is understanding nuclear reactions on radioactive isotopes, for example those produced in the fission of uranium or plutonium. Recently, we have begun a program to measure nuclear reactions on fragments following uranium fission using accelerated radioactive beams of the short-lived isotopes. The present talk will describe this new research program and present the first results.
Viscosity, Black Holes, and Relativistic Heavy Ion Collisions Presenter(s): The University of Tennessee Type: On Demand Air Date: 9/29/2008 Air Time: 3:30 PM EDT Duration: 1 Hour 14 Minutes 44 Seconds September 29th, 2008 - Dam Thann Son, University of Washington	Lance Cooper, University of Illinois Urbana-Champaign Presenter(s): The University of Tennessee Type: On Demand Air Date: 9/22/2008 Air Time: 3:30 PM EDT Duration: 1 Hour 10 Minutes 3 Seconds September 22nd, 2008 - Lance Cooper, University of Illinois Urbana-Champaign
One-Dimensional Atom Wires: Structure Fluctuations and Electronic Instabilities Studied with Scanning Tunneling Microsopy Presenter(s): The University of Tennessee Type: On Demand Air Date: 9/15/2008 Air Time: 3:30 PM EDT Duration: 55 Minutes 12 Seconds September 15th, 2008 - Paul Snijders, Oak Ridge National Lab	NSF Supercomputing: From the Dark Ages to Kraken, and What It Can Do For You! Presenter(s): The University of Tennessee Type: On Demand Air Date: 9/8/2008 Air Time: 3:30 PM EDT Duration: 1 Hour 9 Minutes 25 Seconds Phil Andrews has been involved in supercomputing from the late '70s to the present, when he is now project director for the latest NSF supercomputer to enter production: the University of Tennessee's Kraken system, scheduled to become the world's fastest academic supercomputer next year. He will mention some of his research, beginning at the Princeton Plasma Physics Laboratory, moving through the creation of Mosaic, the first widely used graphics browser, and into medical supercomputing. But the talk will mainly detail the progress, paradigm shifts, successes and other outcomes, from thirty years of National Science Foundation supercomputing, leading up to the current TeraGrid environment with enormous capability for researchers. Physics Colloquium, Monday September 8, 2008 Talk: Room: 307 SERF at 3:30 p.m. Refreshments at 3:00 p.m.
Collective Modes in Unconventional Superconductors Presenter(s): The University of Tennessee Type: On Demand Air Date: 8/25/2008 Air Time: 3:30 PM EDT Duration: 1 Hour 8 Minutes 26 Seconds August 25th, 2008 - Dirk Morr, University of Illinois at Chicago Identifying the collective mode responsible for the emergence of high-temperature superconductivity holds the key to understanding the unconventional properties of the cuprate superconductors. In this talk, I focus on the most likely candidate for the pairing mode, a collective spin mode. In the superconducting state, this mode gives rise to one of the most puzzling phenomena in the high-temperature superconductors, the {\it resonance peak} observed by inelastic neutron scattering experiments. I will argue that this peak arises from a feedback effect of superconductivity on the magnetic excitation spectrum - a feedback effect that reflects the $d_{x^2-y^2}$-wave symmetry of the superconducting gap as well as the topology of the Fermi surface. I will present a number of theoretical studies which show that in the optimally and overdoped cuprates, the experimentally measured momentum and frequency dependence of the resonance peak is consistent with a {\it spin exciton} nature of the resonance, i.e., a particle-hole bound state inside the spin-gap. Moreover, I will discuss a new formalism for computing the spin susceptibility, and in particular the resonance peak, directly from experimental single particle Green's functions derived from angle resolved photoemission spectroscopy. Finally, I will demonstrate that this mode leads to characteristic signatures in the local density of states around impurities that distinguish it from non-magnetic modes. Dirk K. Morr Associate Professor Department of Physics University of Illinois at Chicago 845 W. Taylor St., m/c 273, Chicago, IL 60607 Phone: (312) 996-2237 Fax: (312) 996-9016 e-mail: dkmorr@uic.edu	Honors Day Presenter(s): The University of Tennessee Type: On Demand Air Date: 4/21/2008 Air Time: 3:30 PM EDT Duration: 1 Hour 12 Minutes 12 Seconds
Imaging Hot-Electron Transport Using Chemical Reactions on Metal Surfaces Presenter(s): The University of Tennessee Type: On Demand Air Date: 4/14/2008 Air Time: 3:30 PM EDT Duration: 1 Hour 2 Minutes 5 Seconds Imaging hot-electron transport using chemical reactions on metal surfaces Peter Maksymovych Center for Nanophase Materials Sciences, Oak Ridge National Laboratory, Oak Ridge, TN, 37831 We have investigated a new regime of single-molecule excitation in the scanning tunneling microscope, where hot electrons locally injected from the STM tip spread out via surface resonances over length scales of up to 100 nm and electronically excite surrounding molecules causing chemical reactions. Such non-local reactions were observed for several different molecules on the (111), (110) and (100) terminated surfaces of gold and copper. The hot-electron origin of these reactions was differentiated from the possible electric field effect in the tip-surface junction on the basis of the statistical analysis of the dissociation yield as well as the non-local excitation in the presence of artificially fabricated nanoclusters. One of the new opportunities provided by the non-local excitation is a direct measurement of hot-electron transport on a metal surface. Using a phenomenological kinetic model for the statistical analysis of the non-local reactions, it is shown that the reaction rate increases linearly with tunneling current and decays exponentially with the distance from the excitation pulse. The angular distribution of the reaction events is isotropic on the Au(111) surface, which is consistent with the symmetry of its surface resonances in the energy range of the non-local reaction. Since the attenuation length of the non-local reaction has little dependence on the STM-tip and the parameters of the excitation, we argue that it is proportional to the inelastic mean-free path of hot-electrons in the surface resonance. It is also shown that the total yield of the non-local reaction provides a measure of hot-electron transport across single-atom steps. The reflectance of the hot-electrons by single atom steps on Au(111) was directly measured to be less than 20% at energies above 1.5 V. Talk: 3:30 p.m., 307 Science and Engineering Building Refreshments: 3:00 p.m.	Our latest understanding of the cuprates- some very recent quantum oscillation experiments using the 75 and 85 T magnets at the National High Magnetic Field Laboratory Presenter(s): The University of Tennessee Type: On Demand Air Date: 4/7/2008 Air Time: 3:30 PM EDT Duration: 58 Minutes 5 Seconds Physics Department Colloquium April 7, 2008 John Singleton, National High Magnetic Field Laboratory, Los Alamos National Laboratory Our latest understanding of the cuprates- some very recent quantum oscillation experiments using the 75 and 85 T magnets at the National High Magnetic Field Laboratory Pulsed magnetic fields of up to 85 T and temperatures down to 0.40 K have been used to study single crystals of various cuprate superconductors for several different hole dopings. The samples are measured using a MHz technique that is sensitive to small changes in penetration depth in the superconducting state, and to changes in the skin depth in the normal state. Some experiments also employ torque magnetometers. In the normal state, two or three series of clear magnetic quantum oscillations are observed, periodic in inverse field. The observed frequencies are low (e.g. in YBa2Cu4O8, the frequencies are 200±20 T, 660±15 T and approximately 2400 T) suggesting that the predicted large Fermi surface is broken into smaller pockets due to nesting. The temperature dependence of the oscillations also provides the quasiparticle masses for the Fermi surface sections of the various compounds. In contrast to some predictions, no outstandingly heavy quasiparticles are found; instead, observed masses lie in the approximate range from 2 to 4 times that of the free electron. Our data reveal some general features of the bandstructure of the cuprates and provide information about the doping dependence of the Fermi surface. Consequently, we suggest a nesting scheme that accounts for the evolution of the Fermi-surface topology. Magnetic quantum oscillations are generally recognized to be the most reliable method for deducing the Fermi-surface topology of metals. It is therefore instructive to consider how such data can be reconciled with the results of techniques such as ARPES. By considering the effect of a short antiferromagnetic correlation length ? on the electronic bandstructure and a Fermi-surface topology consistent with the magneticquantum- oscillation experiments, it can be shown that a reduced ? gives an asymmetric broadening of the quasiparticle dispersion, resulting in simulated ARPES data very similar to those observed in experiment. Predicted features include the presence of Fermi arcs close to ak = (p/2, p/2), where a is the in-plane lattice parameter, without the need to invoke a d-wave pseudogap order parameter. Finally, based on the Fermi-surface measurements and neutron scattering data from many different sources, it is possible to propose a magnetically-mediated mechanism for superconductivity in all the cuprates, driven by the topological mapping of the d-wave Cooper-pair wavefunction onto the antiferromagnetic fluctuations that are observed across the whole cuprate phase diagram. Talk at 3:30 p.m., SERF 307 Refreshments at 3:00 p.m.
The Hierarchy of Incompressible Fractional Quantum Hall States Presenter(s): The University of Tennessee Type: On Demand Air Date: 3/31/2008 Air Time: 3:30 PM EDT Duration: 1 Hour 6 Minutes 7 Seconds Physics Department Colloquium Monday, March 31, 2008 John J. Quinn University of Tennessee The Hierarchy of Incompressible Fractional Quantum Hall States The fractional quantum Hall (FQH) effect is the paradigm for all strongly interacting systems. The only energy scale in the problem, the interaction energy of a pair of Fermions, determines everything. Laughlin explained the simplest FQH states in the lowest Landau level (LL0) in terms of the avoidance of electron pair states with the strongest repulsion. These Laughlin correlated electrons (LCEs) give an effective LCE filling factor of unity and an electron filling factor equal to the reciprocal of an odd integer. Jain extended Laughlins picture to include all states which resulted in the LCEs filling an integral number of such levels. LCEs occur only when the interaction energy V(L') of the pairs of Fermions is "superhmonic", i.e. it rises with increasing pair angular momentum L' faster than L'(L'+l), as the value of the pair angular momentum avoided in the LCE state is approached. This requirement is not satisfied at all values of L' for higher Landau levels (LLN, with N > O), nor is it satisfied for all L' for the pseudopotential VQP(L') describing the interaction between Laughlin quasiparticles (QPs). The electron correlations in LLI and the correlations of Laughlin QPs in LL0 can be very different from Laughlin correlations. For example, pairing occurs at certain filling factors even though V(L') is repulsive. Correlations of the most stable FQH states in LLI and of some daughter FQH states of Laughlin QPs in LL0 will be discussed and compared to LCE states in LL0. This work was supported in part by Basic Energy Science of DOE.	Ultrafast Imaging and Holography with X-ray Lasers and Synchrotrons Presenter(s): The University of Tennessee Type: On Demand Air Date: 3/24/2008 Air Time: 3:30 PM EDT Duration: 58 Minutes 40 Seconds Physics Colloquium Monday, March 24, 2008 Stefano Marchesini, LBNL Ultrafast imaging and holography with x-ray lasers and synchrotrons Recent breakthroughs in the development of free-electron lasers now offer the realistic prospect, for the first time, of imaging on the time-scale of atomic motion. Combining this with near-atomic spatial resolution and a non-invasive probe suitable for the life sciences is a huge challenge. The recent development of lensless ("diffractive") X-ray imaging techniques appears to cut this gordian knot by offering diffraction-limited resolution at femtosecond speeds, while taking advantage of the elemental specificity and phase-constrast possibilities of X-ray imaging, combined with adequate pentration. By replacing the necessary lens with a computer algorithm, which solves the famous phase problem to recombine the scattered photons, an aberration-free image may be reconstructed whose resolution is limited in principle only by the X-ray wavelength. These methods have been applied to image object as complex as biological cells, quantum dots, nanaocrystals, and nanoscale aerogel structures. Other test patterns were captured in the fastest flash image ever recorded at suboptical resolution. The simple geometry of lensless imaging however shifts the reconstruction problem to the computational methods. Novel experimental geometries such as massively parallel x-ray holography will be discussed. Physics Colloquium, Monday, March 24, 2008 Talk at 3:30 p.m. in room 307 SERF Building Refreshment at 3:00 p.m., Talk at 3:30 p.m.