51,413 research outputs found
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
Fermion Analogy for Layered Superconducting Films in Parallel Magnetic Field
The equivalence between the Lawrence-Doniach model for films of extreme
type-II layered superconductors and a generalization of the back-scattering
model for spin-1/2 electrons in one dimension is demonstrated. This fermion
analogy is then exploited to obtain an anomalous tail for
the parallel equilibrium magnetization of the minimal double layer case in the
limit of high parallel magnetic fields for temperatures in the
critical regime.Comment: 11 pages of plain TeX, 1 postscript figur
Layered XY-Models, Anyon Superconductors, and Spin-Liquids
The partition function of the double-layer model in the (dual) Villain
form is computed exactly in the limit of weak coupling between layers. Both
layers are found to be locked together through the
Berezinskii-Kosterlitz-Thouless transition, while they become decoupled well
inside the normal phase. These results are recovered in the general case of a
finite number of such layers. When re-interpreted in terms of the dual problems
of lattice anyon superconductivity and of spin-liquids, they also indicate that
the essential nature of the transition into the normal state found in two
dimensions persists in the case of a finite number of weakly coupled layers.Comment: 10 pgs, TeX, LA-UR-94-394
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-
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.
Systematics of one-quasiparticle configurations in neutron-rich Sr, Zr, and Mo odd isotopes with the Gogny energy density functional
The systematics of one-quasiparticle configurations in neutron-rich Sr, Zr,
and Mo odd isotopes is studied within the Hartree-Fock-Bogoliubov plus Equal
Filling Approximation method preserving both axial and time reversal
symmetries. Calculations based on the Gogny energy density functional with both
the standard D1S parametrization and the new D1M incarnation of this functional
are included in our analysis. 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-quasineutron states.Comment: 11 page
Signatures of shape transition in odd-A neutron-rich Rubidium isotopes
The isotopic evolution of the ground-state nuclear shapes and the systematics
of one-quasiproton configurations are studied in odd-A Rubidium isotopes. We
use a selfconsistent Hartree-Fock-Bogoliubov formalism based on the Gogny
energy density functional with two parametrizations, D1S and D1M, and
implemented with the equal filling approximation. We find clear signatures of a
sharp shape transition at N=60 in both charge radii and spin-parity of the
ground states, which are robust, consistent to each other, and in agreement
with experiment. We point out that the combined analysis of these two
observables could be used to predict unambiguously new regions where shape
transitions might develop.Comment: 6 pages, 7 figures. To appear in Phys. Rev. C (Rapid Communications
Microscopic description of quadrupole-octupole coupling in Sm and Gd isotopes with the Gogny Energy Density Functional
The interplay between the collective dynamics of the quadrupole and octupole
deformation degree of freedom is discussed in a series of Sm and Gd isotopes
both at the mean field level and beyond, including parity symmetry restoration
and configuration mixing. Physical properties like negative parity excitation
energies, E1 and E3 transition probabilities are discussed and compared to
experimental data. Other relevant intrinsic quantities like dipole moments,
ground state quadrupole moments or correlation energies associated to symmetry
restoration and configuration mixing are discussed. For the considered
isotopes, the quadrupole-octupole coupling is found to be weak and most of the
properties of negative parity states can be described in terms of the octupole
degree of freedom alone.Comment: 31 pages, 11 figure
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