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

Long-Range Order of Vortex Lattices Pinned by Point Defects in Layered Superconductors

How the vortex lattice orders at long range in a layered superconductor with weak point pinning centers is studied through a duality analysis of the corresponding frustrated XY model. Vortex-glass order emerges out of the vortex liquid across a macroscopic number of weakly coupled layers in perpendicular magnetic field as the system cools down. Further, the naive magnetic-field scale determined by the Josephson coupling between adjacent layers is found to serve as an upperbound for the stability of any possible conventional vortex lattice phase at low temperature in the extreme type-II limit.Comment: 13 pgs., 1 table, published versio

Anomalous Nernst Effect in the Vortex-Liquid Phase of High-Temperature Superconductors by Layer Decoupling

Linear diamagnetism is predicted in the vortex-liquid phase of layered superconductors at temperatures just below the mean-field phase transition on the basis of a high-temperature analysis of the corresponding frustrated XY model. The diamagnetic susceptibility, and the Nernst signal by implication, is found to vanish with temperature as (T_c0 - T)^3 in the vicinity of the meanfield transition at T_c0. Quantitative agreement with recent experimental observations of a diamagnetic signal in the vortex-liquid phase of high-temperature superconductors is obtained.Comment: 8 pages, 3 figure

Pairing gap and in-gap excitations in trapped fermionic superfluids

We consider trapped atomic Fermi gases with Feshbach-resonance enhanced interactions in pseudogap and superfluid temperatures. We calculate the spectrum of RF(or laser)-excitations for transitions that transfer atoms out of the superfluid state. The spectrum displays the pairing gap and also the contribution of unpaired atoms, i.e. in-gap excitations. The results support the conclusion that a superfluid, where pairing is a many-body effect, was observed in recent experiments on RF spectroscopy of the pairing gap.Comment: Journal versio

Berezinskii-Kosterlitz-Thouless Transition in Spin-Charge Separated Superconductor

A model for spin-charge separated superconductivity in two dimensions is introduced where the phases of the spinon and holon order parameters couple gauge-invariantly to a statistical gauge-field representing chiral spin-fluctuations. The model is analyzed in the continuum limit and in the low-temperature limit. In both cases we find that physical electronic phase correlations show a superconducting-normal phase transition of the Berezinskii-Kosterlitz-Thouless type, while statistical gauge-field excitations are found to be strictly gapless. The normal-to-superconductor phase boundary for this model is also obtained as a function of carrier density, where we find that its shape compares favorably with that of the experimentally observed phase diagram for the oxide superconductors.Comment: 35 pages, TeX, CSLA-P-93-

Further analysis of the connected moments expansion

We apply the connected moments expansion to simple quantum--mechanical examples and show that under some conditions the main equations of the approach are no longer valid. In particular we consider two--level systems, the harmonic oscillator and the pure quartic oscillator.Comment: 19 pages; 2 tables; 4 figure

Shape evolution in Yttrium and Niobium neutron-rich isotopes

The isotopic evolution of the ground-state nuclear shapes and the systematics of one-quasiproton configurations are studied in neutron-rich odd-A Yttrium and Niobium isotopes. We use a selfconsistent Hartree-Fock-Bogoliubov formalism based on the Gogny energy density functional with two parametrizations, D1S and D1M. The equal filling approximation is used to describe odd-A nuclei preserving both axial and time reversal symmetries. Shape-transition signatures are identified in the N=60 isotopes in both charge radii and spin-parities of the ground states. These signatures are a common characteristic for nuclei in the whole mass region. The nuclear deformation and shape coexistence inherent to this mass region are shown to play a relevant role in the understanding of the spectroscopic features of the ground and low-lying one-quasiproton states. Finally, a global picture of the neutron-rich A=100 mass region from Krypton up to Molybdenum isotopes is illustrated with the systematics of the nuclear charge radii isotopic shifts.Comment: 21 pages, 14 figures. To be published in Phys. Rev.