No abstract

We investigate superfluidity in the interior-gap states proposed by Liu and Wilczek. At weak coupling, we find the {\em gapless} interior-gap state unstable in physically accessible regimes of the parameter space, where the superfluid density is shown to be always negative. We therefore conclude that the spatially-uniform interior-gap phase is extremely unstable unless it is fully gapped; in this case, however, the state is rather similar to conventional BCS states.Comment: To appear in Physical Review

The energy-level shifts and the change in the rate of spontaneous emission are calculated for an atom located at a distance Z from a dielectric half-space. The dielectric is a non-dispersive and non-absorbing medium characterized by a constant real refractive index n. The explicit analytic formulae derived are applicable for arbitrary values of n. All results are analysed in the non-retarded and retarded limits, which apply to the atom being close to or far from the interface, respectively, i.e. to Z being small or large on the scale of a wavelength of a typical atomic transition. For ground-state atoms, the energy-level shift varies as 1/Z 3 in the non-retarded regime and as 1/Z 4 in the retarded regime, which agrees with the Casimir-Polder result for the limit n → ∞. For excited-state atoms, the energy-level shifts receive additional contributions that oscillate with the distance Z from the interface.

The α-Fe/R2Fe14B-type exchange-coupled NdFeB nanocomposites with a coercivity (iHc) of more than 11 kOe and energy product, (BH)max, of more than 16 MGOe have been successfully obtained on melt spun (Nd0.95La0.05)7.5+xFebalCr2B10 alloy powders, where x ranged from 3 to 3.5. It was found that a slight substitution of Cr for Fe suppresses the formation of the R2Fe23B3 and Fe3B phases during crystallization and results in the formation of an α-Fe/R2Fe14B mixture. Increasing the total rare earth content was found to enhance the remanence, and the Hic of (Nd0.95La0.05)7.5+xFe80.5−xCr2B10 ribbons was also increased drastically with increasing values of x. A Br of 9.2–9.7 kG, Hic of 11.1–13.2 kOe, and (BH)max of 16.5–18.0 MGOe have been obtained on (Nd0.95La0.05)7.5+xFe80.5−xCr2B10 (x=3–3.5).