100,181 research outputs found
Nature of Decoupling in the Mixed Phase of Extremely Type-II Layered Superconductors
The uniformly frustrated layered XY model is analyzed in its Villain form. A
decouple pancake vortex liquid phase is identified. It is bounded by both
first-order and second-order decoupling lines in the magnetic field versus
temperature plane. These transitions, respectively, can account for the
flux-lattice melting and for the flux-lattice depinning observed in the mixed
phase of clean high-temperature superconductors.Comment: 11 pages of PLAIN TeX, 1 postscript figure, published version, many
change
Double fluctuations on the attractive Hubbard model: ladder approximation
We explore, for the first time, the effect of double fluctuations on both the
diagonal and off-diagonal self-energy. We use the T-Matrix equations below
, developed recently by the Z\"urich group (M.H. Pedersen et al) for the
local pair attraction Hamiltonian. Here, we include as well the effect of
fluctuations on the order parameter (beyond the BCS solution) up to second
order in . This is equivalent to approximating the effective interaction
by in the off-diagonal self-energy. For , , and , we find four peaks both for the diagonal,
, and off-diagonal, ,
spectral functions. These peaks are not symmetric in pairs as previously found.
In addition: (a) in , the far left peak has a
vanishing small weight; (b) in the far left and
far right peaks have very small weights. The physical picture is, then, that
the pair physics in the normal phase () is still valid below .
However, the condensation of the e-h pairs produces an additional gap around
the chemical potential as in BCS, in other words, superconductivity opens a gap
in the lower branch of a Hubbard-type-I solution.Comment: LaTeX, 7 pages. 8 figures available on request. To appear in Z.
Physik
Degradation of Phase Coherence by Defects in a Two-Dimensional Vortex Lattice
The thermodynamic nature of two-dimensional vortex matter is studied
theoretically through a duality analysis of the XY model over the square
lattice with low uniform frustration. A phase-coherent vortex lattice state is
found at low temperature if rigid translations are prohibited. It shows a
non-zero phase rigidity that is degraded exclusively by the creation of
dislocation pairs. The unbinding of such pairs causes the vortex lattice to
simultaneously lose phase coherence and to melt at a continuous
(Kosterlitz-Thouless) phase transition. General phase auto-correlation
functions are also computed, and these results are used to argue for the
existence of a continuous melting transition of vortex matter in layered
superconductors.Comment: 11 pgs. of PLAIN TeX, to appear in PRL, some improvement
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