13,602 research outputs found
Thermodynamically stable noncomposite vortices in mesoscopic two-gap superconductors
In mesoscopic two-gap superconductors with sizes of the order of the
coherence length noncomposite vortices are found to be thermodynamically stable
in a large domain of the phase diagram. In these phases the vortex
cores of one condensate are spatially separated from the other condensate ones,
and their respective distributions can adopt distinct symmetries. The
appearance of these vortex phases is caused by a non-negligible effect of the
boundary of the sample on the superconducting order parameter and represents
therefore a genuine mesoscopic effect. For low values of interband Josephson
coupling vortex patterns with can arise in addition to the
phases with , where and are total vorticities in the two
condensates. The calculations show that noncomposite vortices could be observed
in thin mesoscopic samples of MgB.Comment: 5 pages, 3 figures, to be published in Europhysics Letter
Controle integrado da podridão das raÃzes do maracujazeiro Passiflora edulis Simmonds f. flavicarpa Deg.
bitstream/item/88611/1/CPATC-PESQ.-AND.-31-97.pd
Two-species fermion mixtures with population imbalance
We analyze the phase diagram of uniform superfluidity for two-species fermion
mixtures from the Bardeen-Cooper-Schrieffer (BCS) to Bose-Einstein condensation
(BEC) limit as a function of the scattering parameter and population imbalance.
We find at zero temperature that the phase diagram of population imbalance
versus scattering parameter is asymmetric for unequal masses, having a larger
stability region for uniform superfluidity when the lighter fermions are in
excess. In addition, we find topological quantum phase transitions associated
with the disappearance or appearance of momentum space regions of zero
quasiparticle energies. Lastly, near the critical temperature, we derive the
Ginzburg-Landau equation, and show that it describes a dilute mixture of
composite bosons and unpaired fermions in the BEC limit.Comment: 4 pages with 3 figures, accepted version to PR
Berry phases and zero-modes in toroidal topological insulator
An effective Hamiltonian describing the surface states of a toroidal
topological insulator is obtained, and it is shown to support both bound-states
and charged zero-modes. Actually, the spin connection induced by the toroidal
curvature can be viewed as an position-dependent effective vector potential,
which ultimately yields the zero-modes whose wave-functions harmonically
oscillate around the toroidal surface. In addition, two distinct Berry phases
are predicted to take place by the virtue of the toroidal topology.Comment: New version, accepted for publication in EPJB, 6 pages, 1 figur
Fermi-Fermi Mixtures in the Strong Attraction Limit
The phase diagrams of low density Fermi-Fermi mixtures with equal or unequal
masses and equal or unequal populations are described at zero and finite
temperatures in the strong attraction limit. In this limit, the Fermi-Fermi
mixture can be described by a weakly interacting Bose-Fermi mixture, where the
bosons correspond to Feshbach molecules and the fermions correspond to excess
atoms. First, we discuss the three and four fermion scattering processes, and
use the exact boson-fermion and boson-boson scattering lengths to generate the
phase diagrams in terms of the underlying fermion-fermion scattering length. In
three dimensions, in addition to the normal and uniform superfluid phases, we
find two stable non-uniform states corresponding to (1) phase separation
between pure unpaired (excess) and pure paired fermions (molecular bosons); and
(2) phase separation between pure excess fermions and a mixture of excess
fermions and molecular bosons. Lastly, we also discuss the effects of the
trapping potential in the density profiles of condensed and non-condensed
molecular bosons, and excess fermions at zero and finite temperatures, and
discuss possible implications of our findings to experiments involving mixtures
of ultracold fermions.Comment: 12 Pages, 6 Figures and 1 Tabl
Evolution from BCS to BKT superfluidity in one-dimensional optical lattices
We analyze the finite temperature phase diagram of fermion mixtures in
one-dimensional optical lattices as a function of interaction strength. At low
temperatures, the system evolves from an anisotropic three-dimensional
Bardeen-Cooper-Schrieffer (BCS) superfluid to an effectively two-dimensional
Berezinskii-Kosterlitz-Thouless (BKT) superfluid as the interaction strength
increases. We calculate the critical temperature as a function of interaction
strength, and identify the region where the dimensional crossover occurs for a
specified optical lattice potential. Finally, we show that the dominant vortex
excitations near the critical temperature evolve from multiplane elliptical
vortex loops in the three-dimensional regime to planar vortex-antivortex pairs
in the two-dimensional regime, and we propose a detection scheme for these
excitations.Comment: 4 pages with 2 figure
Search for Associations Containing Young stars (SACY): Chemical tagging IC 2391 & the Argus association
We explore the possible connection between the open cluster IC 2391 and the
unbound Argus association identified by the SACY survey. In addition to common
kinematics and ages between these two systems, here we explore their chemical
abundance patterns to confirm if the two substructures shared a common origin.
We carry out a homogenous high-resolution elemental abundance study of eight
confirmed members of IC 2391 as well as six members of the Argus association
using UVES spectra. We derive spectroscopic stellar parameters and abundances
for Fe, Na, Mg, Al, Si, Ca, Ti, Cr, Ni and Ba.
All stars in the open cluster and Argus association were found to share
similar abundances with the scatter well within the uncertainties, where [Fe/H]
= -0.04 +/-0.03 for cluster stars and [Fe/H] = -0.06 +/-0.05 for Argus stars.
Effects of over-ionisation/excitation were seen for stars cooler than roughly
5200K as previously noted in the literature. Also, enhanced Ba abundances of
around 0.6 dex were observed in both systems. The common ages, kinematics and
chemical abundances strongly support that the Argus association stars
originated from the open cluster IC 2391. Simple modeling of this system find
this dissolution to be consistent with two-body interactions.Comment: 17 pages, 7 figs, accepted for publication in MNRA
On topological spin excitations on a rigid torus
We study Heisenberg model of classical spins lying on the toroidal support,
whose internal and external radii are and , respectively. The isotropic
regime is characterized by a fractional soliton solution. Whenever the torus
size is very large, , its charge equals unity and the soliton
effectively lies on an infinite cylinder. However, for R=0 the spherical
geometry is recovered and we obtain that configuration and energy of a soliton
lying on a sphere. Vortex-like configurations are also supported: in a ring
torus () such excitations present no core where energy could blow up. At
the limit we are effectively describing it on an infinite
cylinder, where the spins appear to be practically parallel to each other,
yielding no net energy. On the other hand, in a horn torus () a singular
core takes place, while for (spindle torus) two such singularities
appear. If is further diminished until vanish we recover vortex
configuration on a sphere.Comment: 11 pages, 9 figure
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