Spring 2009 Physics Colloquium Schedule
Unless otherwise noted, the physics colloquia are held in Room 307 of the Science and Engineering Research Facility. Refreshments are served at 3:00 p.m. with the talk following at 3:30. The ORNL Physics Division Seminar Schedule might also be of interest. Professor Michael Guidry is chair of the colloquium program. He may be contacted via e-mail at: guidry@utk.edu.
Physics Colloquium Webcasts
Abstracts
January 12
Peter Armitage, Johns Hopkins University
"Between Electronics and Photonics: Terahertz Investigations of Complex Condensed Matter"
Picosecond (10^-12 sec) timescales are one of the most ubiquitous in condensed matter systems. For example: the lifetime of biologically important collective mode vibrations of proteins, the relaxation times of polar liquids (such as water) due to frustrated molecular rotation, the resonate period of electrons in semiconductors and their nanostructures, the scattering times of electrons in correlated metals, and even the time an electron in Intel's new THz transistor races under the gate; these are all phenomena in the picosecond range.
Such ubiquity makes measurements tools employing Terahertz (10^12 sec) electromagnetic radiation probes potentially quite useful. Unfortunately, this range has been traditionally challenging as it lies in the so-called "terahertz gap" - above the capabilities of traditional electronics, but below that of optical and infrared generators and detectors (photonics). In recent years, however, a number of novel techniques have been developed that span this gap, creating scientific opportunities not widely available previously. I will discuss a number of such measurement possibilities and our application of them to problems as diverse as charge conduction in DNA, electronic glasses, and the 2D superconductor/insulator quantum phase transition. I will concentrate on the new and interesting physics found in these systems, which illustrates not only the power of the instrumentation, but also the wide variety of physical phenomena that can be probed by them.
February 9
Jose Alonso, Sanford Underground Laboratory at Homestake
"Status and Progress at the Sanford Lab 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!
February 16
Raph Hix, ORNL/UT
"The Story Your Atoms Could Tell"
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.
February 23
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).
March 2
Mike Guidry, UT Physics Department/ORNL Physics Division
"Bright Lights, Dark Energy, and a Quite Curious Coefficient: Thermonuclear Supernovae and the Equation of State for the Universe"
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.
March 9
Di Xiao, Oak Ridge National Laboratory Materials Science & Technology Division
"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.
March 23
John Negele, Massachusetts Institute of Technology
"Understanding the Structure of Hadrons Using Lattice QCD"
Understanding how the simple interaction between quarks and gluons gives rise to the rich and complex structure of the protons, neutrons, and other strongly interacting particles that make up most of the mass of the visible universe is one of the great theoretical challenges of our time. This colloquium will provide an elementary introduction to quantum chromodynamics (QCD) and lattice field theory, and show how recent developments in lattice field theory and computer technology are now enabling us to understand basic building blocks of matter from first principles.
March 30
David Blaschke, University of Wroclaw & JINR Dubna
"Constraints on Dense Matter Phases and Equation of State from Compact Stars"
After a short introduction to modern observations of compact stars, which constitute different astrophysical objects such as pulsars, double neutron stars, accreting low-mass X-ray binaries etc., we explain how to extract basic properties (mass, rotation frequency, magnetic field, surface temperature etc.) from these data. In the main body of the talk, we will explain a quantum field theoretical approach to the equation of state (EoS) and transport properties of dense matter with special emphasis on color superconducting quark matter phases and their importance for understanding the phenomenology of compact stars. An outlook is given to the problem of generalizing the EoS to a wide enough range of densities, temperatures and isospin asymmetries in order to apply it for both, supernova collapse simulations and heavy-ion collisions. This is one of the tasks attacked within the research networking programme "Physics of Compact Stars" (2008-2013) of the European Science Foundation.
April 6
Adriana Moreo, UT
"A New Piece in the High Tc Superconductivity Puzzle: Fe based Superconductors"
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.
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.