Ph.D. 1976, University of Illinois, Urbana

Our group's research activity is in theoretical condensed matter (solid-state) physics. Over the last twenty years, my research has encompassed a wide variety of subfields, such as disordered and correlated electronic systems, metal-insulator transitions, doped semiconductors, quantum Hall effect, spin glasses and other random magnetic models, high-temperature superconductors, quantum fluids and solids, charge density waves, and structural phase transitions. Of particular emphasis in recent years has been the study of quantum phase transitions, such as those encountered in doped semiconductors, two-dimensional electron systems in the quantum Hall regime, strongly correlated oxides, and quantum spin systems.

Motion of the nodal points characterizing localized (Ψ5) and extended (Ψ4) electronic states in the quantum Hall rigeme | |

One component of our research effort combines analytical methods, such as the concept of scaling, with numerical methods, such as Monte Carlo simulations, transfer matrix approach, or other matrix techniques to study fundamental issues. For example, recently we have studied (1) phase transitions in various classical and quantum spin glass models and the nature of the spin glass phase; (2) topological properties of localized and extended eigenstates in the integer quantum Hall regime (see figure); and (3) scaling and universality in the quantum Hall regime, to name a few issues. Calculations are carried out on high-performance multiprocessor and massively parallel computers.

Another major area of research is motivated by, and closely related to, experimental systems. In recent years we have studied the many-body physics of disordered systems near a metal-insulator transition, including optical, transport, magnetic, and thermodynamic behavior. Relevant experimental systems include doped semiconductors, metal-insulator mixtures, and expanded metals.

Currently our efforts are directed to the study of electronic properties of materials that do not fall under the purview of conventional band insulators or Fermi-liquid metals, particularly in low dimensions. Thus, for example, we are trying to understand the interplay between charged dopants and magnetic ions in one-dimensional spin-chain compounds, as well as diluted magnetic semiconductors.

Before joining Princeton University, where I also hold an appointment as associate faculty in the Department of Physics, I was head of the theoretical physics research department at Bell Laboratories. I am a fellow of the American Physical Society and was named a J. S. Guggenheim fellow in 1995.