Plutonium and quantum criticality (continued)

be intimately associated with the occurrence of superconductivity is provided by evidence for a spin-glass phase in LaCuO4 doped with strontium. Recently Christos Panagopoulos and Vladimir Dobrosavljevic have used muon spin rotation to show that the spin-glass phase in LaCuO4 doped with strontium extends all the way from zero hole doping to a hole doping near to optimal doping for superconductivity, i.e., roughly in the middle of the superconducting region. Thus it appears quite plausible that there is an intimate connection between the quantum fl uctuations associated with the spinglass phase and high-Tc superconductivity. Of course, one may hesitate to claim that spinorbit localization is responsible for the spinglass phenomena in high-Tc superconductors because it is diffi cult to justify why spin-orbit effects should be important in the cuprates. On the other hand, there is little doubt that such effects could be important in the actinides, and a theory of spin-orbit localization may be just what is needed to understand the quantum critical properties of plutonium. Spin-orbit localization of charge carriers does not by itself imply that there is a gossamer condensate. However, it turns out that it is very natural for spin-orbit localized carriers with opposite spin to be paired, and one can explicitly write down the condensate wave function. Very recently direct evidence for the appearance in plutonium of a condensate that may be similar to the gossamer condensate in the high-Tc cuprates has been provided by studies of the effect of alpha decay damage in plutonium on the magnetization carried out at Livermore by Fluss and McCall. Both α and δ plutonium have large temperature-independent magnetic susceptibilities that increase with time at low temperatures.
Isochronal annealing experiments show that these increases are connected with the radiation damage of the lattice. However, the dominant contribution to the magnetic susceptibility at early times corresponds to an electronic bubble whose size is considerably larger than expected from quantum Monte Carlo calculations of the damage cascades. The temperature dependence of the susceptibility of these bubbles fi ts well to a Curie–Weiss law, with possibly a small Neel temperature, indicative of localized antiferromagnetic fl uctuations. The occurrence of such bubbles is natural if one is near to a QCP like that shown in the fi gure on page 11. This would be a quantum analog of the familiar mixed phases that appear in classical gases near to their critical point. I would like to close by exhibiting an exact solution to the nonlinear Schrödinger equation that describes the condensate ground state for the charge carriers in a three-dimensional layered conductor when the spin-orbit localization length is smaller than the screening length. This wave function describes a fl uid of magnetic monopole-like carriers

describes the distances between carriers using complex coordinates zi within each plane, and f (z )is an analytic function of the z j j . The function f (z ) describes the natural tendency for the pairing of these charge carriers by virtue of the fact that magnetic monopoles with opposite magnetic charge attract This work was performed in part under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under contract No. W-7405-Eng-48.
This article was contributed by George Chapline of the Physics and Advanced Technology Directorate, Lawrence Livermore National Laboratory. The author thanks Jim Smith, Mike Fluss, Scott McCall, Kevin Moore, Christos Panagopoulos, David Santiago, Montu Saxena, Gil Lonzarich, and Jan Zaanen for helpful conversations.

next article... "Postdoc's poster chosen for oral presentation "