Colloquium Schedule
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Unless otherwise noted, the physics colloquia begin with refreshments at 3:00 p.m. in Room 307 of the Science and Engineering Research Facility (SERF Building), with the talk following at 3:30 p.m. Colloquium Contact: Dr. Hanno Weitering
Fall 2002
| Date | Speaker and Topic |
|---|---|
| August 26 | Prof. Piers Coleman Center for Materials Theory, Rutgers University Title: Quantum Criticality: New Frontier in Strongly Correlated Materials Contact: Soren Sorensen |
| September 2 | No Colloquium (Labor Day) |
| September 9 | Prof. Vladimir Ignatovich Joint Institute for Nuclear Research, Dubna, Russia Contact: Yuri Kamyshkov |
| September 16 | Prof. Kunimitsu Uchinokura University of Tokyo, Japan Contact: Pengcheng Dai |
| September 23 | Dr. J. Crow (Frontiers in Materials Lecture) Director National High Magnetic Field Laboratory/Florida State University Contact: E. Ward Plummer |
| September 30 | Christian Y. Cardall Physics Division, Oak Ridge National Laboratory Contact: Mike Guidry |
| October 7 | Premi Chandra NEC Research Laboratory, Princeton Title: From Roman Vases to Novel Memories and Beyond: Thoughts on the Glass Transition Contact: Soren Sorensen |
October 14 | Prof. Jing Shi University of Utah Title: Exploring Nanomagnetism with Imaging and Transport Contact: Hanno Weitering |
| October 21 | Dr. Jeffrey W. Lynn Team Leader, NIST Center for Neutron Research National Institute of Standards and Technology Title: Magnetic Superconductors: Exceptions to the Rule Contact: Pengcheng Dai |
| October 28 (CANCELLED) | Dr. M.J. Clark National Radiological Protection Board, UK Title: Connecting the Gravitational Constant G to Other Physical Constants Contact: Al Sanders |
| November 4 | Dr. Pengcheng Dai UT Physics Title: Probing Magnetism in Strongly Correlated Electron Systems with Neutrons Note: Prof. Peter Ecklund of Penn State University was originally scheduled for November 4 but will speak at a January 20, 2003, colloquium instead. |
| November 11 | Prof. Dunghai Lee University of California at Berkeley Title: Inhomogeneity in doped Mott insulator and its role in high temperature superconductors |
| November 18 | Prof. Isao Shimamura Institute of Physical and Chemical Research (RIKEN)- Japan Title: Dynamics of Antiprotonic Atoms |
| November 25 | Dr. Klaus Peters Experimentelle Kern- und Teilchenphysik Ruhr-Universität Bochum, Germany Contact: Ted Barnes |
| December 2 | J. Michael Ramsey Corporate Research Fellow and Group Leader Laser Spectroscopy and Chemical Microtechnology Oak Ridge National Laboratory Contact: Hanno Weitering |
Abstracts
Piers ColemanCenter for Materials Theory
Rutgers University
In the sixties and seventies, the theoretical community was profoundly shaken by the discovery of universality in statistical mechanics- a realization that the critical physics of water, magnetism and superfluidity could all be linked within a single conceptual framework. The ramifications of this revolution have since been felt far and wide throughout physics.
In this talk I shall describe how the ideas of classical criticality are being transformed into the domain of the quantum, where they are known as "quantum criticality". Quantum criticality is important for material science because it influences broad regions of the material phase diagram at finite temperatures. During the last half decade it has become possible to fine tune these materials to quantum criticality- a point at zero temperature where critical fluctuations of the magnetization or some other order parameter develop in both space and time. From the theoretical perspective, this phenomenon is exciting because the properties of the metallic state at the the quantum critical point appear to be described by a completely new class of universality. I shall describe the experiments that lead us to this conclusion and some of the radical new ideas that are circulating concerning its ultimate resolution.
Dr. Vladimir K. Ignatovich
Joint Institute for Nuclear Research
JINR/Dubna/Russia
Ball lightning. Neutron starts. What is in common?
We show that two absolutely different phenomena are related by a simple physical principle.
The ball lightning can be modelled by a shock wave containing photons, which are held inside due to the total internal reflection at the shock wave front. At the same time the photons hold the shock wave frozen by their electrostrictive forces created by optical potential of the light - matter interaction.
In the same fashion the neutron star is a set of neutrons that hold the star from spreading by the neutron striction forces. We show that these forces become stronger than gravity forces, when radius of the star is less than 40 km (according to present day theories the neutron star has radius of about 10 km). It means that if we suddenly switch off the gravity field, the neutron star will remain compact.
We point out that these striction forces can lead to some interesting phenomena in Bose-Einstain condensate.
See ref. Ignatovich V.K., Electromagnetic Model of Ball Lighting. (1992)-v.2, N.6., Laser Physics., p.991-996.
Prof. Kunimitsu Uchinokura
Department of Advanced Materials Science, The University of Tokyo
Impurity-induced ordered phases in quasi-one-dimensional spin-gap systems
The discovery of the spin-Peierls transition in inorganic compound CuGeO3 revived or produced intensive studies of spin-Peierls phenomenon and also the physical properties of CuGeO3 itself.This was made possible because very good and large single crystals of CuGeO3 can be grown by the floating zone method in contrast to organic spin-Peierls mateials previously studied. The other very important point is that the impurity-induced antiferromagnetic phase was found in this material. This phenomenon, i.e., a magnetic phase is induced by the (nonmagnetic) impurities into the singlet spin-gap system, is really a new one. This has been studied by our group as well as many groups in the world and many of the new properties have been revealed. Then a problem arised to us whether this phenomenon is unique to the S=1/2 spin-gap system or not. Another typical spin-gap system is Haldane-gap system with S=1 spins. We searched for a new Haldane-gap-phase meterials (because there had not been any reports on the impurity-induced ordered phase in known Haldane-gap materials) and found that PbNi2V2O2 has the Hadane gap and also found that it has the inpurity-induced ordered state. Thus we have shown that this phenomenon is a common property in S=1/2 and S=1 quasi-one-dimensional spin-gap systems.
I would like to talk only briefly on CuGeO3 (because too many facts have been known) and show the experimental results on PbNi2V2O2 in detail.
Reviews concerned with this problem:
K. Uchinokura, J. Phys.: Condensed Matter. {14} (2002) R195, ``Spin-Peierls transition in CuGeO3 and impurity-induced ordered phases in low-dimensional spin-gap systems"
K. Uchinokura and T. Masuda, In ``Frontiers in Magnetism", J. Phys. Soc. Jpn. {69} (2000) Suppl. A 287, ``Impurity-induced antiferromagnetic phases in quasi-one-dimensional spin-gap systems with S=1/2 and S=1 spins"
K. Uchinokura, Prog. Theor. Phys. Suppl. {145} (2002) 294-305. Proceedings of the 16th Nishinomiya Yukawa Memorial Symposium and the YITP Workshop on Order, Disorder and Dynamics in Quantum Spin Systems, ``Impurity-induced ordered phases in quasi-one-dimensional spin-gap systems"
Dr. J. Crow
National High Magnetic Field Laboratory/Florida State University
High Magnetic Fields: Frontiers in Condensed Matter Science
The National High Magnetic Field Laboratory (NHMFL) was established by the National Science Foundation and charged to develop and support unique facilities to advance magnet related research in all areas of science and engineering. Many experimental approaches rely on magnetic field to probe the fundamental electronic, magnetic and structural properties of nature. Facilities such as those developed at the NHMFL and open to all qualified scientist and engineers are critical to understanding the physical properties new materials and have also impacted the growth of new materials.. In addition, the magnetic field is one of the thermodynamic parameters along with pressure, temperature and concentration that control the equilibrium state of matter. Thus, high magnetic fields provide the added feature that they can alternate the thermodynamic state of matter and this capability often provides significant insight into the physics of condensed matter systems. A few obvious examples include the suppression of the ordered state in superconductors and antiferromagnetic systems, quantization of electronic states, electronic level crossing in spin systems, and many others. The presentation will review the role played by high magnetic fields in the study of condensed matter systems and will briefly explore some of the opportunities for the future.
* Research at the NHMFL is supported by the NSF Cooperative Agreement No. DMR-0084173 and the State of Florida.
Christian Y. Cardall
Physics Division, Oak Ridge National Laboratory
Core-collapse Supernovae: Phenomenological Bonanza, Computational Challenge Core-collapse supernovae are amazing displays of astrophysical fireworks---and the optical emission is only a tiny part of the story! These events involve virtually all branches of physics and spawn phenomena observable by every kind of astronomical observation. This richness of theory and observation presents a formidable challenge to their understanding via computer simulations, but the TeraScale Supernova Initiative promises to usher in a new era of realism and maturity in modeling the key processes of collapse and explosion.
Premi Chandra
NEC Research Institute, Princeton
From Roman Vases to Novel Memories and Beyond: Thoughts on the Glass Transition Glass is a non-equilibrium state of matter that persists on millenium time-scales; this dramatic violation of the ergodic hypothesis remains an outstanding challenge in statistical mechanics. A glass is an intrinsically non-random solid that is structurally disordered. Unlike either a liquid or a crystal, its low-temperature properties depend on sample history, thereby putting it well outside the framework of equilibrium theory. As a step towards developing an Ising model for this ubiquitous phenomenon, I will present current efforts to develop theories of disorder-free glassiness that are experimentally verifable. It is anticipated that the detailed study of intrinsically non-random glasses will lead to insights in other areas, including content-addressable data storage, optimization algorithms and error-correcting codes, and I shall give a concrete example of such a link. I will end with a discussion of quantum systems in liquid and in glassy states, indicating how the study of such problems is crucial towards the design, development and control of quantum circuitry.
Prof. Jing Shi
University of Utah
Exploring Nanomagnetism with Imaging and Transport
When the linear dimension of magnetic structures is below the submicron exchange length, both quasi-static and dynamic magnetization reversal behaviors become rather rich and complex. In addition, the high spin-polarized current density (~10^8A/cm^2) exerts additional exchange torque on the spins of the magnetic layers, yielding more interesting
dynamic phenomena. These fundamental nanomagnetism issues
profoundly affect the performance of the high-density magnetic recording and memory devices. Employing magnetic force microscopy (MFM) and photo-emission electron microscopy (PEEM), we have studied unique magnetization reversal properties of the magnetic nanostructures fabricated using electron beam lithography (EBL). We have gained a good understanding of the role of magnetization vortices and nucleation in magnetization reversal. Furthermore, we have also studied the effect of the magnetostatic interaction in nano-element arrays using PEEM imaging. In the second part of my talk, I will present our recent work on the exchange torque due to the spin-transfer effect in EBL-patterned magnetic structures.
Dr. Jeffrey W. Lynn
NIST Center for Neutron Research
National Institute of Standards and Technology
The effects of magnetic impurities and the possibility of magnetic ordering in superconductors has had a rich and interesting history. Early work showed that magnetic impurities substituted into a superconductor quickly suppress superconductivity due to the strong spin scattering that disrupts the Cooper pairs. The first exceptions to this rule were provided by the ternary Chevrel-phase superconductors (RMo6S8) and related (RRh4B4) compounds, which exhibited long range magnetic order that coexisted with superconductivity The magnetic ordering temperatures were low, and the antiferromagnetism had only a weak influence on the superconducting state. Similar behavior is observed for the rare earth magnetic order in the cuprates (e.g RBa2Cu3O7) and borocarbides (RNi2B2C), which are all antiferromagnets. One of the most interesting aspects of the cuprates concerns the magnetism associated with the Cu spins, which is believed to cause the d-wave superconducting pairing and can also simultaneously order magnetically. In the rare and more interesting situation where the magnetic interactions are ferromagnetic, there is strong coupling to the superconducting state that originates from the internally generated magnetic field. The competition with the superconducting order parameter gives rise to long wavelength oscillatory magnetic states and/or reentrant superconductivity in the ternary superconductors such as HoMo6S8. This behavior will be contrasted with results on the new “ferromagnetic superconductors” such as RuSr2GdCu2O8, UGe2, and ErNi2B2C. If time permits, we will also discuss recent measurements and properties of the strongest electron-phonon coupled superconductor, Mg B2.
Dr. M.J. Clark (CANCELLED)
National Radiological Protection Board, UK
It is usually assumed that the Newtonian gravitational constant G (kg -1 m3 s -2) is independent of all other fundamental constants, except during the Planck (Big Bang) era. Hence the relevance of G to the rest of physics is slight. Using phenomenological models for virtual graviton exchange between mass-energy, it can be shown that G is connected to Planck's constant h, the speed of light c and a dimensionless coupling constant ag outside the Planck era. The models are based on quantum field theory concepts: one is based on a straightforward summation of all possible exchange pathways between atomic mass-energy units uc2, while another uses a model devised by H A Bethe for the interaction of radiation with matter. The applications and implications of the derived formulation
will be examined. Using the models, a prediction emerges for experimental values of G to increase with increasing temperature of the attracting mass.
Dr. Pengcheng Dai
UT Physics
Probing Magnetism in Strongly Correlated Electron Systems with Neutrons
For many decades it has been accepted that the low-temperature transport properties of most semiconductors and metals can be described by Landau's Fermi liquid theory, where the states of an interacting electron gas in the material can be put into a one-to-one correspondence with those of a non-interacting gas of "quasi-particles". The properties of recently discovered new (and in some cases, old) materials appear to defy Landau's description and are dominated by strong electron-electron, electron-lattice, and electron-orbital interaction effects. Examples for this class of so-called "highly correlated electron materials" include the high-transition-temperature copper oxide superconductors, heavy fermion metals, and colossal magneto-resistance manganese oxides. Clearly, highly correlated electron systems present some of the deepest intellectual challenges in physics and magnetism seems to play a central role. Neutron scattering, with its unique capability for studying spin and charge ordering, has contributed significantly to our understanding of these materials. In this colloquium, I will discuss what neutrons can do and give examples to show how neutron scattering has provided unique information concerning these materials and fundamentally changed our view about the properties of highly correlated electron systems.
Prof. Dunghai Lee
University of California at Berkeley
Inhomogeneity in doped Mott insulator and its role in high temperature superconductors
I introduce the concept that there are two generic classes of Mott insulators in nature. They are distinguished by their responses to weak doping. Doped-charges form clusters (i.e. distribute inhomogeneously) in type-I Mott insulators whereas they distribute homogeneously in type-II Mott insulators. I will also present my opinion on the role inhomogeneity plays in the cuprate superconductors.
Dr. Isao Shimamura
RIKEN (Institute of Physical and Chemical Research)
Hirosawa 2-1, Wako, Saitama 351-0198, Japan
Dynamics of Antiprotonic Atoms
Antiprotonic atoms, a kind of exotic atoms, are the atoms in which an electron is replaced by an antiproton, or the antiparticle of the proton. The antiprotonic atoms may be regarded as peculiar diatomic molecules with a pair of positive-charge and negative-charge "nuclei," and have extraordinary properties. They are in resonance states, rather than in stable bound states. Just after an antiprotonic atom is formed in a collision of an antiproton with an ordinary atom, the antiproton is in an orbital with a large principal quantum number (around ~40), and then cascades down to lower and lower orbitals via various atomic processes, such as radiative transitions, Auger-electron emission, and collisions with ambient species. The antiproton decays when it encounters the nucleus in the antiprotonic atom, the lifetime against the decay being usually of the order of picoseconds. For a few percent of antiprotonic helium only, and not for any other kind of antiprotonic atoms, the lifetime is six orders of magnitude longer. Recent experimental findings about and theoretical understanding of these strange exotic atoms, their formation process, and the atomic processes they experience before their decay will be discussed in comparison with the much-better-known dynamics of ordinary atoms.
Dr. Klaus Peters
Experimentelle Kern- und Teilchenphysik
Ruhr-Universität Bochum, Germany
The GSI Future Project
GSI (http://www.gsi.de) plans a new accelerator facility for the research with ion and antiproton beams, in cooperation with their users and the international community. With the new project, GSI aims to provide scientists in Europe and the world with an outstanding accelerator and experimental facility for studying matter at the level of atoms, atomic nuclei, protons and neutrons as the building blocks of nuclei - and part of a wider family called hadrons - and the subnuclear constituents called quarks and gluons (see http://www.gsi.de/GSI-Future/eng) . The heart of the new facility is a superconducting synchrotron double ring facility with a circumference of about 1,100 meters. A system of cooler-storage rings for effective beam cooling at high energies and various experimental halls will be connected to the facility. The accelerator will yield ion beams with highest beam intensity and also higher beam energies. Moreover, the facility offers the possibility to provide high quality beams of antiprotons and ions for the experimental program. The facility will cover the following main topics
- Nuclear Structure Physics,
- Physics with Antiprotons,
- Nuclear Matter Physics,
- Plasma Physics,
- Atomic Physics and
- Applications
[1] An International Accelerator Facility for Beams of Ions and Antiprotons,
Conceptual Design Report, GSI 2001
J. Michael Ramsey
Chemical Sciences Division
Oak Ridge National Laboratory
Micro- and Nanofabricated Devices for Chemical and Biochemical Experimentation
Tremendous interest in microfabricated fluidic channel structures (microchips) has grown over the past decade due to the large number of powerful demonstrations that have appeared in the literature. The diversity of chemical and biochemical measurement techniques implemented on microchips is large including various electrophoretic and chromatographic separations, chemical and enzymatic reactions, noncovalent recognition interactions, sample concentration enhancement, and cellular manipulations. In addition the types of samples addressed by microchips has been broad in scope, e.g., small ions and molecules, single and double stranded DNA, amino acids, peptides, and proteins. These devices have low cost and small footprints while consuming miniscule quantities of reagents and producing rapid results. Moreover, the manufacturing strategy used to make these devices, i.e., photolithography, allows highly parallel systems to be fabricated at low incremental cost. All of these features suggest the possibility to perform chemical experimentation at a massive scale at low cost on a bench top. More recently we have been investigating the prospects of shrinking channel lateral dimensions by a factor of ˜ 1000, i.e., to molecular length scales. A number of interesting capabilities are possible with nanoscale channels and pores including the structural characterization of single molecules. Fundamental studies of electrokinetic fluid transport in nanoconfined spaces have been investigated allowing the first experimental benchmarking of continuum theories for such phenomena that were developed decades ago. In addition, potential applications of devices with ˜ 100 nm features have been demonstrated. Some of our latest results in these areas of research will be presented.
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