73,368 research outputs found
Fermion Pairing across a Dipolar Interaction Induced Resonance
It is known from the solution of the two-body problem that an anisotropic
dipolar interaction can give rise to s-wave scattering resonances, which are
named as dipolar interaction induced resonaces (DIIR). In this letter, we study
zero-temperature many-body physics of a two-component Fermi gas across a DIIR.
In the low-density regime, it is very striking that the resulting pairing order
parameter is a nearly isotropic singlet pairing and the physics can be well
described by an s-wave resonant interaction potential with finite range
corrections, despite of the anisotropic nature of dipolar interaction. The
pairing energy is as strong as a unitary Fermi gas nearby a magnetic Feshbach
resonance. In the high density regime, the anisotropic effect plays an
important role. We find phase transitions from singlet pairing to a state with
mixed singlet and triplet pairing, and then from mixed pairing to pure triplet
pairing. The state with mixed pairing spontaneously breaks the time-reversal
symmetry.Comment: 4.5 pages, 4 figures, figures updated, minor changes in tex
Superconducting properties of Gd-Ba-Cu-O single grains processed from a new, Ba-rich precursor compound
Gd-Ba-Cu-O (GdBCO) single grains have been previously melt-processed successfully in air using a generic Mg-Nd-Ba-Cu-O (Mg-NdBCO) seed crystal. Previous research has revealed that the addition of a small amount of BaO2 to the precursor powders prior to melt processing can suppress the formation of Gd/Ba solid solution, and lead to a significant improvement in superconducting properties of the single grains. Research into the effects of a higher Ba content on single grain growth, however, has been limited by the relatively small grain size in the earlier studies. This has been addressed by developing Ba-rich precursor compounds Gd-163 and Gd-143, fabricated specifically to enable the presence of greater concentrations of Ba during the melt process. In this study, we propose a new processing route for the fabrication of high performance GdBCO single grain bulk superconductors in air by enriching the precursor powder with these new Ba rich compounds. The influence of the addition of the new compounds on the microstructures and superconducting properties of GdBCO single grains is reported
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