A perturbative approach to J mixing in f-electron systems: Application to actinide dioxides

We present a perturbative model for crystal-field calculations, which keeps into account the possible mixing of states labelled by different quantum number J. Analytical J-mixing results are obtained for a Hamiltonian of cubic symmetry and used to interpret published experimental data for actinide dioxides. A unified picture for all the considered compounds is proposed by taking into account the scaling properties of the crystal-field potential.Comment: 16 pages + 4 figures; will appear http://prb.aps.or

A Dynamical Study of the Non-Star Forming Translucent Molecular Cloud MBM16: Evidence for Shear Driven Turbulence in the Interstellar Medium

We present the results of a velocity correlation study of the high latitude cloud MBM16 using a fully sampled $^{12}$CO map, supplemented by new $^{13}$CO data. We find a correlation length of 0.4 pc. This is similar in size to the formaldehyde clumps described in our previous study. We associate this correlated motion with coherent structures within the turbulent flow. Such structures are generated by free shear flows. Their presence in this non-star forming cloud indicates that kinetic energy is being supplied to the internal turbulence by an external shear flow. Such large scale driving over long times is a possible solution to the dissipation problem for molecular cloud turbulence.Comment: Uses AAS aasms4.sty macros. Accepted for publication in Ap

Proposal for an Optical Test of the Einstein Equivalence Principle

The Einstein Equivalence Principle (EEP) underpins all metric theories of gravity. Its key element is the local position invariance of non-gravitational experiments, which entails the gravitational red-shift. Precision measurements of the gravitational red-shift tightly bound violations of the EEP only in the fermionic sector of the Standard Model, however recent developments of satellite optical technologies allow for its investigation in the electromagnetic sector. Proposals exploiting light interferometry traditionally suffer from the first-order Doppler effect, which dominates the weak gravitational signal necessary to test the EEP, making them unfeasible. Here, we propose a novel scheme to test the EEP, which is based on a double large-distance optical interferometric measurement. By manipulating the phase-shifts detected at two locations at different gravitational potentials it is possible to cancel-out the first-order Doppler effect and observe the gravitational red-shift implied by the EEP. We present the detailed analysis of the proposal within the post-Newtonian framework and the simulations of the expected signals obtained by using two realistic satellite orbits. Our proposal to overcome the first-order Doppler effect in optical EEP tests is feasible with current technology.Comment: manuscript improve

Enhancement of rare-earth--transition-metal exchange interaction in Pr2_{2}Fe17_{17} probed by inelastic neutron scattering

The fundamental magnetic interactions of Pr$_{2}$Fe$_{17}$ are studied by inelastic neutron scattering and anisotropy field measurements. Data analysis confirms the presence of three magnetically inequivalent sites, and reveals an exceptionally large value of the exchange field. The unexpected importance of $J$-mixing effects in the description of the ground-state properties of Pr$_{2}$Fe$_{17}$ is evidenced, and possible applications of related compounds are envisaged.Comment: 4 RevTeX pages, 4 EPS figures. Accepted for publication by Appl. Phys. Lett. (will be found at http://apl.aip.org

Unexpected phase locking of magnetic fluctuations in the multi-k magnet USb

The spin waves in the multi-k antiferromagnet USb soften and become quasielastic well below the antiferromagnetic ordering temperature TN. This occurs without a magnetic or structural transition. It has been suggested that this change is in fact due to dephasing of the different multi-k components: a switch from 3-k to 1-k behavior. In this work, we use inelastic neutron scattering with tridirectional polarization analysis to probe the quasielastic magnetic excitations and reveal that the 3-k structure does not dephase. More surprisingly, the paramagnetic correlations also maintain the same clear phase correlations well above TN (up to at least 1.4TN)