Professor Joseph Brill
Condensed matter physics is the study of the properties of materials formed when large numbers of atoms are condensed into the liquid and solid states. The continuing growth of this field reflects the variety of novel properties which occur when many particles are brought together. Among the surprising new materials observed during the past decade are organic and high-temperature superconductors, high conductivity polymers, ``heavy fermion'' metals, semiconductor systems that exhibit the quantum Hall effect and fractional charges, and the Buckminsterfullerenes, which are completely new phases of carbon. The 1980s also witnessed the discovery of the scanning tunneling microscope, a table-top instrument with sub-atomic resolution. Since expansion of the technology of this field depends crucially on the ability to synthesize, understand, and manipulate new materials, condensed matter physicists often find valuable collaborations with chemists and engineers. To these collaborations the physicist brings insight into the quantum mechanical basis of the atomic interactions, and expertise with a host of probes used to study these interactions in detail.
Theorists at the University of Kentucky are studying the static and dynamic properties of a variety of materials, such as semiconductor and metal clusters, fullerenes, and transport in quantum microstructures, using first-principles quantum mechanical calculations. The goal of this work is to produce a truly microscopic understanding of the structure and bonding properties of solids, as well as to allow a prediction of the properties of new systems. The results of these calculations are compared with known structures and binding energies, as well as with measured electronic and optical properties. The bonding and chemistry of such complicated structural systems as coal are also being analyzed. Statistical mechanical methods are being used to determine alloy phase diagrams, simulate electrical conduction in heterogeneous and disordered media (the percolation problem), elucidate the kinetics of structural changes, and model the Josephson tunnelling between grains of ceramic high temperature superconductors. The University of Kentucky provides a variety of computers, ranging from microcomputers to supercomputers which are used extensively to develop an understanding of the properties of condensed systems.
Another area of investigation in condensed matter physics involves the properties of systems that are extremely small. The study of these has been in part driven by the demand for smaller and faster components in electronic systems, and it is believed that controlling the properties of these microstructures may lead, for example, to a new generation of ultrasmall and ultrafast computers. The study of microstructures has produced many new discoveries in basic physics -- the quantum Hall effect, electron solids, universal conductance fluctuations-- because physical properties at such small size scales are largely determined by the particle-wave duality inherent in the quantum-mechanical structure of nature.
Collaborative studies between theorists and experimentalists at the University of Kentucky explore the properties of novel materials such as intercalated graphite, charge-density-wave conductors, and high temperature superconductors. Processes such as sintering and charge-density-wave depinning are numerically simulated as well as studied in the laboratory.
Ongoing experimental studies of crystals include those with novel electronic
systems such as ``heavy fermion'' and ``low-dimensional'' (i.e., highly
anisotropic) metals. In heavy fermion metals, the electrons respond to external
probes as if they had masses up to several hundred times the free electron
mass, giving rise to unusual magnetic and superconducting behavior. The
structural and electronic anisotropies of low-dimensional metals give rise to a
number of unusual properties. Materials studied include intercalated graphite
compounds, organic and high temperature superconductors, and charge and
spin-density wave metals. In the latter, the electronic charge or spin
densities are modulated with wavelengths of the order of a few atomic spacings.
Experiments on these systems include transport studies under high pressure or
magnetic field, optical and Raman spectroscopy, and measurements of the
specific heat, magnetic susceptibility, and electro-acoustic and
magneto-acoustic properties. Solids containing fullerene (
)
molecules are being studied in close collaboration with members of the
chemistry department; in these novel materials, the fullerenes act like (huge!)
atoms of a new element.
Tunnelling spectra of semiconductors and superconductors are also being studied, principally with the scanning tunnelling microscope. Of particular interest are spectral studies of the interfaces between metals and semiconductors, and between normal metals and superconductors, such as at magnetic vortices. Thin films are of increasing technological importance as electronic components, optical filters, and thermal, chemical, and mechanical coatings. At UK, we are studying the optical and electronic properties and applications of a number of metal oxide films, which range from insulators to superconductors, and wide-gap semiconducting films, such as those made from diamond.
Experimental facilities within the Department include a low temperature scanning tunnelling microscope for both imaging and tunnelling spectroscopy; a Faraday balance and vibrating sample magnetometer; a Raman spectrometer; infrared, visible, and ultraviolet spectrophotometers; a powder x-ray diffractometer; superconducting magnets which provide fields of up to 9T; a low temperature differential scanning calorimeter; programmable resistive furnaces for crystal growth up to 1700 C; arc furnaces; thin film deposition systems using both electron-beam and resistive evaporation as well as RF and magnetron sputtering; systems for low frequency acoustic (0-100kHz) and high pressure experiments; and numerous crysotats, including a 50 mK dilution refrigerator. In addition, collaborations with members of the nuclear physics group, the Chemistry Department, the Engineering School (including the UK Center for Materials Characterization) and the Consortium for Fossil Fuel Liquefaction allow ready access to facilitites such as EXAFS at Brookhaven National Laboratory, Rutherford backscattering and other nuclear analytical probes, single-crystal x-ray diffraction, chemical vapor deposition, and scanning and transmission electron microscopy.
The size of the solid state group allows for a wide range of research interests, while maintaining close interactions among faculty and students. Graduate students share and benefit from these interactions, and are expected to achieve a wide appreciation of the field. Condensed matter physics seminars are held weekly during the academic year; in addition to talks by visitors, many seminars are presented by UK faculty and students about both their own research and new developments in condensed matter physics. There are also many ``Materials Science Seminars'', held jointly by the condensed matter physics group and other materials-related research groups on campus.
Faculty and Research Staff