1992 McCoy Award Recipient
Nicholas J. Giordano
Professor of Physics

Behavior of electrons in ultra-small structures and statistical mechanics

The recipient of the Herbert Newby McCoy Award for 1992 is Nicholas J. Giordano, professor of physics. Professor Giordano is a condensed matter physicist whose interests include the behavior of electrons in ultra-small structures and statistical mechanics. He was an undergraduate at Purdue and did his graduate work at Yale, where he obtained his Ph.D. in 1977. After a brief stint on the faculty at Yale, he returned to Purdue in 1979. He was an Alfred P. Sloan Foundation Fellow from 1979 to 1983 and is a Fellow of the American Physical Society. In addition to physics, his interests include running and music.

Abstract of Talk
The technology that has brought digital watches to your wrist and powerful computers into your home has been powered in large part by advances in the fabrication of small electronic circuits. Current technology routinely produces transistors and other components with sizes of a few micrometers (about one-tenth of the diameter of a human hair). This technology has been fueled in part by more advanced techniques that now are capable of producing structures nearly a factor of 1,000 smaller than those found in present-day integrated circuits. These state-of-the-art techniques are of practical interest, since they likely will form the basis for future generations of microelectronics. They are also of interest from a fundamental point of view, since they make possible the fabrication and study of physical systems whose sizes are intermediate between microscopic (i.e., atomic) and macroscopic; this regime has become known in recent years as "mesoscopic." Experiments over the past decade have shown that these systems exhibit a variety of novel properties. 1VIany of these properties illustrate (and depend on) the quantum mechanical behavior of electrons; in this sense, the ability to assemble structures whose behavior is closely dependent on quantum mechanics makes it fair to refer to a worker in this field as a "quantum mechanic." This talk will be a description of some of the ultra-small structures that have been studied in recent years, and will include discussion of a few of the fundamental physical phenomena that they have been used to explore. The emphasis will be on work being done at Purdue and on prospects for the future.

Research
Most physical phenomena possess a characteristic length scale. For example, water droplets that fall from a faucet all have the size of a few millimeters, which is determined by properties of water, such as surface tension. Likewise, many phenomena found in condensed matter have their own characteristic lengths. These length scales often are not apparent when one considers the properties of a "bulk" (i.e., large-scale) system. However, if one makes the size of the system comparable to the characteristic length scale of a particular phenomenon, then it is often the case that the phenomenon will be strongly modified, and the behavior will be very different from that found in a corresponding bulk system. For processes involving electron motion (i.e., electrical conduction), the characteristic length scales are commonly in the range of 10-1,000 nanometers (1 nm = 10-9 m). Hence, for the size of the system to have an effect on the electrical properties it requires the fabrication of systems in this size range. Nicholas Giordano has spent the past decade studying conduction processes in ultra-small metallic structures. This work has been made possible by the development of several methods for fabricating structures with one or more lateral dimensions of 10-1,000 nanometers. In his first work within this area, Giordano studied the influence of quantum mechanical interference effects on the electrical conductivity of one- dimensional metals. These effects cause the conductivity to exhibit interesting dependences on temperature and magnetic field. These effects also make the conductance extremely sensitive to the location of every impurity in the system. The motion of only a single impurity can yield a sizable change in the conductance, and Giordano's group was the first to observe this effect in metallic structures. In more recent work, Giordano and co-workers have examined a number of other problems. Topics that have been studied include superconductivity in one dimension, the effect of microwave fields on electron coherence, and the behavior of magnetic impurities in one- and two-dimensional metals. In all of these cases, the behavior is affected greatly by making the system size comparable to the relevant characteristic length scales. This has led to new insight into these fundamental problems.