Lattice defects and magnetic ordering in plutonium oxides: a hybrid density-functional-theory study of strongly correlated materials.

Experimental studies of actinide oxides are challenging, and conventional electronic structure calculations fail to qualitatively reproduce the scarce data. We employ a new generation of hybrid density functionals to model a defective plutonium dioxide lattice. The procedure is first tested against stoichiometric bulk PuO2 and Pu2O3, for which predictions agree well with experiment where known. The interstitial oxygen in PuO2.25 is found to be singly charged, consistent with experimental observations and contrary to the O2- previously proposed theoretically.

Intensity dependence of photoassociation in a quantum degenerate atomic gas.

We have measured the intensity dependent rate and frequency shift of a photoassociation transition in a quantum degenerate gas of 7Li. The rate increases linearly with photoassociation laser intensity for low intensities, whereas saturation is observed at higher intensities. The measured rates and shifts agree reasonably well with theory within the estimated systematic uncertainties. Several theoretically predicted saturation mechanisms are discussed, but a theory in which saturation arises because of quantum mechanical unitarity agrees well with the data.