CWRU Physics Faculty
Rolfe G. Petschek
Professor of Physics
S.B., Massachusetts Institute of Technology (1975)
Ph.D., Harvard University (1980)
Condensed Matter Theory, Optical Materials
My group is interested primarily in organic materials which are disordered (glassy or liquid) or partially ordered (liquid crystalline). These materials present interesting problems in statistical physics, quantum physics, and optics. In addition, a number of such materials have either proven themselves to be, or have good prospects for becoming, important in displays, optical computing, optical connections between electronic circuits, and other optical and opto-electronic devices.
A wide variety of structures with interesting properties are currently available, and potentially even more can be made. These include rod-like molecules, disk-like molecules, polymers consisting of many such molecules bonded together in various ways, molecules dissolved in glasses etc. We use analytic and numerical tools of statistical mechanics and quantum mechanics, symmetry analysis, and extensive discussions with near-by experimentalists in order to discover new principles which control the statistical or optical properties of the wide variety of actual or potential structures. For example, rod-like molecules with flexible tails form layered structures known as smectic liquid crystals at temperatures which depend on the length of such molecules. Such structures are rather flexible and scatter light appreciably. However, if such molecules are tied together (head to tail) to form a polymer, the system can be shown to be considerably less flexible and to scatter much more weakly. This behavior does not depend strongly on the flexibility of the molecule, a result found using an analytic argument based on a field theory of chain statistics. The theory of this system is quite similar to (and has appreciable impact on) the properties of flux lines in high temperature superconductors. Similar quantitative or qualitative changes have been found in such quantities as the surface tension. If two rather different molecules are bonded together, the nature of the state, and its opto-electronic properties, can change radically as the new structure may become ferroelectric. We have studied this sort of behavior in conjunction with synthetic chemists and experimental physicists, and have used the numerical Monte Carlo method in the process adding to known methods for computing free energy differences. If such molecules are bonded together to form a three dimensional network (or gel), the resultant properties are again radically different. In this case the theory is similar to, and expands upon, the theory of disordered magnets.
Thus our work is simultaneously both applied and basic, with impact on electro-optic and optical technologies, and with impact on the tools with which physicists study the world.