Physics Colloquium Schedule

Spring 2004

Abstracts (as made available)

Pairing vs Laughlin Correlations and Hierarchies of Incompressible Quantum Liquid States

John Quinn (UT Professor of Physics and Lincoln Chair of Excellence)

Laughlin correlations among interacting Fermions of a 2D system in an applied magnetic field mean maximum avoidance of pair states with the smallest pair separations (and the largest pair angular momentum L'). Such correlations occur only if the pseudopotential V(L'), defined as the interaction energy of a pair as a function of L', is "superharmonic". By this we mean that V(L') increases with L' faster than L'(L'+1). Because this is not the case in excited Landau levels, states like frequency= 7/3, 5/2, and 8/3 do not support Laughlin correlations. The pseudopotentials V_QP-_QP(L') of quasiparticles can be determined (up to an unimportant constant) from numerical studies of small systems. For QP's of the Laughlin frequency = 1/3 state, the "subharmonic" form of V_QP-_QP(L') forbids Laughlin correlations at certain values of the QP filling (e.g., frequency_QE = 1/3 and frequency_QH = 1/5). Instead, the QP's tend to form pairs in order to minimize the pair amplitude at the most repulsive (but not the largest) values of L'. A simple model assuming complete pairing together with Laughlin correlations among the pairs yields incompressible states at the unexpected values of frequency observed recently by Pan et al. ¹

Perspectives on Neutrino Physics and Astrophysics

Baha Balantekin (University of Wisconsin, Madison)

This talk will first explore the physics potential of solar neutrino and related reactor and atmospheric neutrino experiments. It will concentrate on three different areas of physics that can be probed in these experiments: i) Neutrino Physics: Doing global analyses of the existing data to determine neutrino mass and mixings; ii) Solar Physics: Measuring solar temperature and density in these experiments; iii) Nuclear Physics: In particular measuring the weak axial two-body current. Examples will be given for these three different areas. In the latter part of the talk the implications of the findings of these experiments on r-process nucleosynthesis in core-collapse supernovae will be highlighted.

Nucleus as a Quantum Many-Body System

Thomas Papenbrock (UT Physics/ORNL)

There has been considerable progress in microscopic nuclear structure theory over the last decade. Ab initio calculation with realistic interactions and large-scale shell model calculations with accurate effective interactions now provide a much-improved and predictive description of light and medium mass nuclei. With the advent of the rare isotope accelerator, interest is shifting away from the valley of stability toward drip-line nuclei. As the model spaces for these nuclei grow rapidly in size, it is important to find efficient coupling schemes. I describe the status of the field and present two new approaches: the density matrix renormalization group and the wave function factorization method. In the last part I switch from the nucleus to another strongly correlated quantum many-body system, and discuss some of the interesting properties of dilute atomic gases of hard-core bosons.

Pure and Applied Studies in Vibrational Spectroscopy: Raman Under Liquid Nitrogen and Atmospheric Physics

Bob Compton (UT Physics/UT Chemistry) and Stewart Hager (UT Physics)

Raman and infrared (IR) spectroscopy provide complementary information on molecular vibrations. Selection rules for the light-matter interaction require that asymmetric vibrations are excited in IR absorption and symmetric vibrations are active in Raman scattering. Together these spectroscopies have been essential techniques used for the structural analysis of organic and inorganic molecules since the 1930's. Following the discovery of the Raman effect in 1928 by C.V. Raman, Raman spectroscopy has proven to be a powerful tool for the characterization of molecular structure. Raman spectroscopy is especially useful for the analysis of biological systems and nanomaterials. Recording Raman spectra for many molecules in air at room temperature is difficult or impossible as a result of sample degradation due to a combination of laser heating and oxidation. We have developed a simple method to overcome these problems by performing Raman spectroscopy under liquid nitrogen, a technique we call RUN. The lower temperature provides ro-vibrational cooling and allows for recording higher resolution spectra with less congestion. The Physics Department at UT has a long history in Infrared spectroscopy beginning with the efforts of Alvin Nielsen. As a continuation of this tradition, we will also describe a new facility for performing high-resolution IR spectroscopy which employs a DA-8 Bomem FTIR coupled to a long-path White cell. Infrared spectroscopy of atmospheric gases is used to study atmospheric changes and to detect new IR absorbing species in the various layers of the Earth's delicate atmosphere. Dr. Hager will describe a new facility at UT which employs the Sun as the IR light source designed to study the time and altitude dependence of various Greenhouse gases in the atmosphere. This will include a discussion of atmospheric line fitting techniques.

Making Semiconductors Magnetic

Steven Erwin (Naval Research Laboratory)

Spintronics, or spin-electronics, is a new field of science and technology based on control of the electron through both its spin and charge degrees of freedom. One possible avenue to realizing this goal is to develop new materials that are simultaneously semiconducting and magnetic. The so-called "dilute magnetic semiconductors" do precisely this -- conjoining, in a single material, the twin advantages of magnetic nonvolatility and bandgap engineering.

In most dilute magnetic semiconductor systems, ferromagnetism results from substitutional doping by magnetic ions such as Mn. In addition to providing localized spins, Mn is electrically active as an acceptor, and generates holes that mediate an indirect exchange interaction that leads to the ferromagnetic ground state. This talk will describe how this happens from a theoretical perspective, and what can go wrong in practice. Finally, a strategy will be described for developing new materials with magnetic and electronic properties that can be tailored as needed.

Novel Physics in the Copper-Oxide High-Temperature Superconductors

Yoichi Ando (Central Research Institute of Electric Power Industry, Japan)

In 1986, Bednorz and Muller (who won the Nobel Prize in the following year) discovered high-temperature superconductivity in a copper oxide. Since then, condensed-matter physicists have been struggling hard to understand why the superconductivity occurs at such high temperature (up to 160 K) in copper oxides, but the understanding is still far from being satisfactory --- in fact, the mechanism of the high-temperature superconductivity remains one of the biggest unsolved problems in the contemporary physics. In this talk, I will introduce some of the fascinating new physics in the copper oxides, such as electron self-organization in a striped manner and curious magnetic shape memory effects, and discuss how these novel features might be relevant to the occurrence of the high-temperature superconductivity.

Scientific Ethics: the Responsibilities of Institutions, Professional Societies, Journals, and Scientists

Martin Blume (The American Physical Society)

Attention to scientific ethics tends to ebb and flow, with spectacular cases of plagiarism, data fabrication or conflict of interest heightening that attention. Such heightening also leads to more accusations of misconduct, as scientists are emboldened to raise concerns that they might, in quieter times, avoid stating. The scientific community, especially in physics, has been faced recently with a series of problems on an international scale that hae demanded attention. In this talk examples of these problems will be discussed, along with guidelines for handling them. There are still ethical problems for which guidelines need to be developed, and these will be considered as well.

It is clear that the scientific community must deal seriously with these cases - scientists insist on it, and the public, which supports most scientific research, demands it.

• APS Guidelines for Professional Conduct (also contains links to other
  worthwhile sites): http://www.aps.org/statements/02_2.cfm
• IUPAP Workshop on Scientific Misconduct (and links contained therein):
  http://www.iupap.org/working/workshop.shtml
• Council of Science Editors Retreat on Misconduct:
  http://www.councilscienceeditors.org/events/retreats.cfm

• Report of the APS Task Force on Ethics
• Report of the Council of Science Editors Retreat

Superfluidity, Phase Coherence and the New Bose-Condensed Alkali Gases

Tony Leggett (University of Illinois, 2003 Nobel Laureate)

The phenomenon of superfluidity was discovered in liquid helium nearly sixty years ago, and ever since, following the almost immediate suggestion of Fritz London, it has been the almost universal belief in the condensed-matter community that it is due to the onset of the phenomenon of Bose-Einstein condensation which is theoretically predicted to occur in that system at sufficiently low temperature. However, for various practical reasons, it is extremely difficult even to establish unambiguously that BEC is occurring in 4-He, let alone to test directly some of the ideas which connect it to superfluidity. The recent attainment of BEC in dilute atomic alkali gases opens a new arena in this respect, allowing us to do many experiments which we would have loved to do in 4-He but which are in practice unfeasible in that system. In this talk I first review briefly the fundamental ideas developed in the helium context, then give a general introduction to the physics of the BEC alkali gases, and finally discuss some of the novel posibilities they open up,both already realized and still on the drawing-board.

Discovery of the Pentaquark: An Exotic Baryon

Ken Hicks (Ohio University)

The pentaquark is a fundamental particle made up of 4 quarks and one antiquark, as compared with baryons (3-quarks) and mesons (quark-antiquark) which encompass virtually all known strongly-interacting particles. Although pentaquarks, along with other multi-quark particles, can exist by the rules of QCD, none had been found before last year when one called the Q+ was announced by an experimental collaboration working at the SPring-8 facility in Japan. The Q+ is composed of 2 up quarks, 2 down quarks, and 1 anti-strange quark. It was predicted in 1997 by theoretical calculations using the chiral soliton model. The SPring-8 discovery sparked a number of other experimental announcements by ITEP, CLAS and SAPHIR collaborations. This talk will describe the theoretical motivation, the subsequent announcements by SPring-8 and CLAS collaborations (the speaker is a member of both experiments), and the theoretical speculations that followed. The announcement of the pentaquark received wide media coverage, some calling it a "new classification of matter." The implications of this "exotic baryon matter" will be discussed.

The Search for the Quark Gluon Plasma

Ken Read (UT/ORNL)

What are we learning from relativistic heavy ion collisions concerning QCD at extremely high energy densities, possible new states of matter, and conditions in the early universe? Lattice QCD studies predict that a novel state of matter, the Quark Gluon Plasma, should exist at extremely high energy densities. Such a state would consist of deconfined quarks and gluons. The Relativistic Heavy Ion Collider at BNL was constructed to explore this domain of energy densities far above those of normal cold nuclear matter. Ultrarelativistic collisions of heavy ions are used to recreate conditions in the laboratory similar to those of the early universe. Recent results indicate that a hot, dense medium with strong final state effects is indeed being created in ultrarelativistic Au+Au collisions. We review the current status and outlook as work continues to further clarify the properties of the medium that is observed and to address alternate explanations.

What If Academic Physics Were a Business?

John S. Rigden (Washington University in St. Louis)

Fresh ideas can come from thinking about old problems in new ways. Physics is a mature scientific discipline with an earned reputation. If physics is what physicists do, then the reputation of physics is inaccurate and it does not serve the best interests of its academic practitioners. A helpful way to think about academic physics is in business terms. If we do this, ideas emerge which, with little effort, can benefit departments of physics in many ways.

Note: See Dr. Rigden's article on "The Business of Academic Physics" online at Physics Today: http://www.physicstoday.org/vol-56/iss-11/p45.html.

Our Explosive Origins: Probing Stellar Cataclysms with Radioactive Nuclear Beams

Michael S. Smith (Physics Division, Oak Ridge National Laboratory)

Some stars end their lifecycles in violent explosions which synthesize and disperse elements - including those that make life possible - into space. A frontier area of research involves utilizing beams of radioactive nuclei to improve our understanding of these explosions and the implications on cosmic element production. Thermonuclear reactions on proton-rich radioactive isotopes are important in the explosive hydrogen burning that powers nova explosions and X-ray bursts, and reactions on neutron-rich radioactive nuclei are responsible for the heavy element production occurring in supernovae. At ORNL's Holifield Radioactive Ion Beam Facility (HRIBF), we are measuring these reactions on radioactive nuclei to probe the details of these cataclysmic cosmic events. Our precision results with beams of radioactive fluorine isotopes have helped resolve important uncertainties in a number of hydrogen-burning thermonuclear reactions. We have also made the first neutron transfer measurement on a nucleus in the r-process path, demonstrating the viability of an important technique for nuclear astrophysics studies at next generation radioactive beam facilities. Details of our synergistic research program studying stellar explosions, involving measurements, data evaluations, and element synthesis calculations, will be given, as well as prospects for the future of this exciting field at the Rare Isotope Accelerator (RIA).

Brute-Force Quantum Computation

Gabriel Aeppli (University College of London, UK)

We use the methods of solid state physics to show experimentally that quantum mechanics can be useful for computation.

Exotic Nuclei: Unique Laboratory of Nuclear Structure

Jacek Dobaczewski (Warsaw University/Visiting UT/ORNL Professor)

Proposed and existing experimental facilities--those that aim at intense production and study of nuclei far from stability--pose new challenges and opportunities for nuclear structure theory. Even if qualitative predictions of properties of exotic nuclei can be obtained by extrapolating those of stable systems, new phenomena are expected, and more robust theoretical approaches have to be developed.