ICAM Theme
Dr. Herb Mook
Oak Ridge National Laboratory
Solid State Division, 1 Bethel Road
Oak Ridge, TN 37831
(423) 574-5242
(423) 574-6268 FAX
There are a number of topics that could be addressed by the CAM approach. We have been working using neutron scattering with several systems that display non-Fermi liquid behavior. The first of these is the Y(1-x)U(x)Pd3 system in which we have collaborated with Brian Maple to find the origin of the non-Fermi liquid behavior by examining the temperature dependence of the magnetic scattering (PRL 75,1202, 1995). We find that for concentrations of U in the 0.45 range the material orders magnetically, but that this order occurs at lower and lower temperatures as the U concentration is reduced. At the 0.2 concentration where non-Fermi liquid behavior is observed the magnetic transition is driven to zero temperature with only fluctuations being observed even at very low temperatures. The origin of the non-Fermi liquid behavior could thus be characterized in terms of a T=0 quantum phase transition.
Parallel experiments on the high Tc superconductors have been made to understand the magnetic scattering for these materials. We have again in these materials non-Fermi liquid behavior at least in the normal state. Here the low temperature state is superconductivity so that we can not address the quantum critical point directly, however, scaling behavior found in the normal state can be understood in terms of a nearby quantum critical point (Science, 21, 1432, 1997).
The idea of a quantum critical point may thus be used to understand a number of physical systems whose microscopic details are quite different but which display universal critical behavior. There may be analogs to the scaling observed in highly correlated electron systems to that observed in polymer solutions as they are cooled, resulting in a diverging correlation length for concentration fluctuations as the critical demixing point is approached. In these materials the critical phenomena is altered by a characteristic length scale that competes with the correlation length of the concentration fluctuations.