Candidate CAM Systems: Quantum Phase
Transitions
Professor Elihu Abrahams
Rutgers University
Department of Physics & Astronomy
New Brunswick, NJ 08903
(732) 445-2520
(732) 445-4400 FAX
Quantum mechanics is essential to describe phase transitions which occur at temperatures below some characteristic relevant energy of the system in question. In particular, zero temperature phase transitions are quantum phase transitions, characterized by a quantum critical point. These occur, for example, in some diluted magnetic systems and metal-insulator transitions are in general of this type.
A zero temperature phase transition is examined by varying some control parameter, for example, the density of some impurity. One then finds that by only slight variations in the control parameter, one induces dramatic changes in the low temperature properties of the system; for example, metal vs. insulator.
The approach to a phase transition is characterized by fluctuations in an appropriate order parameter (e.g. magnetization for magnets, conductance for metal-insulator systems). For ordinary thermodynamic phase transitions that occur at non-zero temperature, these fluctuations occur over a length scale that becomes longer and longer as the critical point is approached. At quantum phase transitions, in addition to the diverging length scale, there is a diverging time scale that describes the duration of the quantum fluctuations between different quantum states. Thus, the statics and dynamics are intrinsically coupled and must be treated together. An examination of system properties over a wide range of length and time scales is essential for a complete understanding.
The metal-insulator transition is an excellent example of a quantum phase transition. There have been recent experiments on semiconductor devices that have revealed new mysteries about the subject.
Suggestions for ICAM Workshop or Discussion.
Areas in which there could be immediate overlap of interests of people from different disciplines are those of instrumentation, measurement technique and sample/materials preparation. It is probable that interactions among people from different fields would follow quite naturally from a workshop devoted to, for example, measurement techniques for experiments involving varying time scales. Another topic would be the exploration of what joint experimental and materials facilities might usefully be developed.
Since I am not an experimentalist, I do not have the expertise to flesh out these topics. However they seem to me to be useful topics for discussion which could lead to not only to new research problems but which might result in concrete proposals for ICAM facilities.