Theoretical

The condensed matter theory group (Efros, Mattis, Raikh, Rashba, Sutherland, Wu) is highly productive and interacts closely with the solid state experimental groups. Current topics being studied include disordered systems with interacting electrons, percolation theory, 2-D electron gas, the integer and fractional quantum Hall effect, electronic properties of disordered semiconductors (including microstructures), and hopping magnetoresistance. In addition, extensive work on the "few-body problem," high-Tc superconductivity, and Fermi liquid theory in 1, 2, and 3 dimensions is ongoing. Phase transitions and critical phenomena, soliton modes, and chaotic behavior, are other foci of the theory group. Quasiperiodicity in solids (first conceived by Penrose in his mathematical investigations of tiling, then later found by diffraction analysis to naturally exist in certain crystals) is also being investigated.

Experimental

The Physics Department has a large and diverse program in the area of experimental solid state physics. One group (Taylor, Ohlsen, G. Williams, Worlock) has been devoted to the study of the physical properties of disordered semiconductors such as amorphous silicon and chalcogonide glasses, as well as on the peculiar ordering of ternary III-V crystalline alloys (which has profound effects on their electronic properties). In addition, the electronic and structural stability of hydrogenated amorphous silicon film is being investigated. A variety of experimental techniques are employed in these studies, including nuclear magnetic resonance, electron paramagnetic resonance, and optically detected magnetic resonance techniques.

The optical properties of solids are also being studied (Vardeny, Luty, Gellerman). Picosecond pulsed laser systems are used to study the ultrafast response of conducting polymers (organic chains with remarkable properties, including in some cases the existence of excitations with sub-integral charge), semiconductors, amorphous solids, fullerenes (the exotic carbon balls, e.g. C60, named after Buckminster Fuller), and high-Tc superconductors. Research is also being done in the nonlinear optical properties of solids as applied to fast optical switches (which may well constitute the logic gates of future generations of computers).

Utah is recognized as one of the leaders in the development of tunable infrared lasers, which are being used here to study the electronic properties of various types of defects in insulating ionic and molecular solids. These defects are in part being explored as potential "memory elements" for use in future high density optical information storage devices.

Much of the optical research is done at the Dixon Laser Institute of the University of Utah, formed in 1984 to facilitate collaborations in laser applications research among the Colleges of Science, Engineering, and Medicine. The institute provides experimental research support for visiting scholars and serves as a center for the discussion of optical effects in a variety of materials. In addition, this Institute will play an important role in the Department's Medical Physics Program (see below). Besides encouraging novel interdisciplinary research programs, this Institute provides centralized, shared laser resources that expand the potential of each individual researcher.

Low-temperature research (Symko) is primarily focused on macroscopic quantum tunnelling in long Josephson junctions using a 3He-4He dilution refrigerator, and on fluxon dynamics in long junctions. This is of importance in the applications of long Josephson junctions in ultra high speed electronics; such junctions are fabricated for high frequency oscillators. Single electron tunnelling in mesoscopic junctions is also being investigated. The application of the thermoacoustic effect to refrigeration (cooling with sound waves) is also being developed for electronic devices.

An investigation of a wide range of surface phenomena is being performed with the newly developed Scanning Probe Microscopies (C. Williams). These studies range from the nanometer scale visualization and measurement of the properties of semiconductors and insulators to the visualization of single molecules. These new microscopies (atomic force microscopy, scanning capacitance microscopy, electrostatic force microscopy, etc.) are related to the scanning tunnelling microscope (STM) which is capable of imaging the surface structure of solids at the single atom level. These techniques, some of which are being developed in the Physics Department, have tremendous potential for application in nearly all the physical sciences. Currently, investigations are being performed to study impurities and charged defects in semiconducting systems and electrostatic charge effects on the chemical properties of molecular systems.

Pioneering research in NMR techniques and applications to solid-state physics and medical physics (see (6) below) is being done in our department (Ailion). In particular, NMR research is being performed on two particular classes of disordered solids: (1) incommensurate solids (which have perfect long range order but not lattice periodicity and are thus intermediate between perfectly ordered crystals and completely disordered systems) and (2) ferroelectric glasses, which can show spin disorder but lattice periodicity. Equipment available for this research includes two 15" (0-2.5T) electromagnets and one 8.5T superconducting magnet along with three complete pulsed NMR spectrometers and computers.