Brown

Discussion for ICAM Workshop

Stuart Brown

University of California at Los Angeles

Department of Physics

405 Hilgard Avenue

Los Angeles, CA 90024

Physical scientists have always operated on the premise that general concepts are the most powerful. Nevertheless, topics investigated by condensed matter physicists have multiplied to include a large number of distinct subjects. Under such conditions, it can often happen that concepts developed in one area are independently worked out for another instead of adapted directly. Further, even in my subfield of correlated electrons, there is often less communication than similarities in the physics of different systems might warrant. If the new Institute can improve the culture of communication between scientists of different subfields and install a motivation in graduate students to think as broadly as possible, its impact will be significant.

Possible topics for addressing by the Institute of Complex Adaptive Matter

Experimental paths for producing conductors from half-filled correlated electron systems.

The creation of conducting molecular charge-transfer salts was intensely pursued in the 1980's and 1990's. An important benefit to the field was the combined efforts of synthetic chemists and condensed matter physicists who merged their talents to produce materials in which an enormous variation of interesting cooperative phenomena was observed, including superconductivity, antiferromagnetism, Spin-Peierls, charge-density wave, and field-induced spin-density waves. The materials are low-dimensional and half-filled, and their physical properties are tunable by high-pressure. For example, many that are insulating can be made to be conducting by pressure application. In many ways, the electronic properties are similar to that produced in doped oxides, such as the cuprate superconductors. I believe there is a great potential to improve our understanding of the effects of dimensionality and correlations to compare, in detail, properties of the two types of systems.

Disorder effects on classical and quantum phase transitions.

A triumph in condensed matter physics is the progress made in understanding the properties of phase transitions, particularly those which are continuous. More recently, a great deal of attention has been paid to the effects of continuous quantum phase transitions on finite temperature properties. Experimentally, less is understood about the effects of disorder on the quantum transitions than for many finite temperature phase transitions. At the same time, quite a few disordered systems exhibit non-Fermi liquid behavior which could be associated with nearby quantum phase transitions between competing ground states. A comprehensive examination of the effects of disorder could contrast the role of disorder on finite temperature transitions in various condensed matter systems and quantum phase transitions.