Dr. James R. ThompsonProfessor
Ph.D., Duke University, 1969
Office: 406-A Nielsen Physics Building
Phone: 865-974-7837 or 865-574-0412 (ORNL)
CONDENSED MATTER PHYSICS
Superconducting materials: current conduction, vortex dynamics, and characteristic length scales
High temperature superconductors are fascinating materials with great fundamental interest and significant technological potential. Thompson maintains a vigorous, interactive program of research to understand better a broad spectrum of phenomena; topics of interest include both high Tc materials and superconductors that are novel due to nanoscale confinement, e.g., due to quantum controlled growth, unusual crystallographic structure, or other physical features. Many of these studies are based on magnetic investigations, exploring the intimate and complex interrelationship of (1) thermal disordering energy, (2) the interaction energy between quantized lines of magnetic flux (vortices) in a superconductor, and (3) the "pinning" energy that tends to trap vortices at localized defects.
These energy scales are frequently comparable in magnitude in high-Tc superconductors, meaning that vortices can move with relative ease. As motion of a vortex inevitably dissipates energy, it is essential to immobilize the vortices, if electric current conduction is to be loss-free. The study of vortex dynamics is providing a rich testing ground for novel theoretical and experimental concepts. Thompson has explored the formation and understanding of "tailored defects" with controlled densities and morphologies, for trapping or "pinning" vortices; this tilts the balance of energies in the material to enhance its current-carrying capability ("critical current density"), sometimes by orders-of-magnitude. These pinning sites have been formed by many methods, including ionizing radiation, deliberate non-stoichiometry to form precipitates, chemical formation of columnar-like structures via self-assembly of BaZrO3 nanoparticles, and topological defects in quantum controlled growth of ultrathin elemental and alloy films. A complementary line of study systematically establishes the equilibrium length scales for various families of superconductors, which is essential knowledge for understanding the materials.
Other classes of solids have unusual and varied magnetic properties as
well. These include nano-composites containing a fine dispersion of paramagnetic
or ferromagnetic particles, suspended in an insulating matrix. As a second
example, several cuprate (and other) compounds exhibit complex internal
ordering of magnetic species; bulk magnetic studies provide insight into
the materials and complement microscopic studies, such as neutron scattering
Brief VitaProfessor James R. Thompson earned the B.S. degree in Physics at Davidson College in 1964; he then completed the Ph.D. degree in Physics at Duke University in 1969, studying condensed matter at low temperatures. He joined the faculty at the University of Tennessee in Knoxville in 1971. Since 1978, Thompson has held a (now Senior) Adjunct Scientist appointment in the Materials Science and Technology Division at the Oak Ridge National Laboratory, collaborating in studies of conventional and high-Tc superconductors and other materials. He spent a leave-of-absence at the Nuclear Research Center in Karlsruhe, Germany, developing and exploring amorphous metallic alloys. Also, he frequently makes shorter research visits to a number of international laboratories, with which he maintains active collaborations. Thompson is a Fellow of the American Physical Society. He was lead author on a US Department of Energy award for solid state research with "Significant Implications for Energy Related Technologies." Also, he is a recipient of a UTK Chancellor's Research Award for Research and Creative Activity, an ORNL Significant Event Award, and a “Nano-50 Award” by Nanotech Briefs (co-recipient with ORNL collaborators, November, 2006). In summary, Thompson maintains an active experimental program in condensed matter physics and is coauthor of more than 270 scientific publications.