4,849 research outputs found
Superfluid phases of triplet pairing and neutrino emission from neutron stars
Neutrino energy losses through neutral weak currents in the triplet-spin
superfluid neutron liquid are studied for the case of condensate involving
several magnetic quantum numbers. Low-energy excitations of the multicomponent
condensate in the timelike domain of the energy and momentum are analyzed.
Along with the well-known excitations in the form of broken Cooper pairs, the
theoretical analysis predicts the existence of collective waves of spin density
at very low energy. Because of a rather small excitation energy of spin waves,
their decay leads to a substantial neutrino emission at the lowest
temperatures, when all other mechanisms of neutrino energy loss are killed by a
superfluidity. Neutrino energy losses caused by the pair recombination and
spin-wave decays are examined in all of the multicomponent phases that might
represent the ground state of the condensate, according to modern theories, and
for the case when a phase transition occurs in the condensate at some
temperature. Our estimate predicts a sharp increase in the neutrino energy
losses followed by a decrease, along with a decrease in the temperature, that
takes place more rapidly than it would without the phase transition. We
demonstrate the important role of the neutrino radiation caused by the decay of
spin waves in the cooling of neutron stars.Comment: 24 pages, 5 figure
Transient heat and mass transfer analysis of supercritical cryogenic storage systems with spherical static heaters Final report
Transient heat and mass transfer analysis of supercritical cryogenic storage systems with spherical static heaters by computer progra
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A Systemic Approach to Music Performance Learning with Multimodal Technology
Bosonization for disordered and chaotic systems
Using a supersymmetry formalism, we reduce exactly the problem of electron
motion in an external potential to a new supermatrix model valid at all
distances. All approximate nonlinear sigma models obtained previously for
disordered systems can be derived from our exact model using a coarse-graining
procedure. As an example, we consider a model for a smooth disorder and
demonstrate that using our approach does not lead to a 'mode-locking' problem.
As a new application, we consider scattering on strong impurities for which the
Born approximation cannot be used. Our method provides a new calculational
scheme for disordered and chaotic systems.Comment: 4 pages, no figure, REVTeX4; title changed, revision for publicatio
Miscibility in a degenerate fermionic mixture induced by linear coupling
We consider a one-dimensional mean-field-hydrodynamic model of a
two-component degenerate Fermi gas in an external trap, each component
representing a spin state of the same atom. We demonstrate that the
interconversion between them (linear coupling), imposed by a resonant
electromagnetic wave, transforms the immiscible binary gas into a miscible
state, if the coupling constant, , exceeds a critical value, . The effect is predicted in a variational approximation, and
confirmed by numerical solutions. Unlike the recently studied model of a binary
BEC with the linear coupling, the components in the immiscible phase of the
binary fermion mixture never fill two separated domains with a wall between
them, but rather form anti-locked ( -phase-shifted) density waves.
Another difference from the bosonic mixture is spontaneous breaking of symmetry
between the two components in terms of numbers of atoms in them, and
. The latter effect is characterized by the parameter (only is a conserved quantity), the
onset of miscibility at meaning a transition
to . At , features damped
oscillations as a function of . We also briefly consider an asymmetric
model, with a chemical-potential difference between the two components.Comment: 9 pages, 12 figures, PRA (in press
Vortex dynamics in superconducting channels with periodic constrictions
Vortices confined to superconducting easy flow channels with periodic
constrictions exhibit reversible oscillations in the critical current at which
vortices begin moving as the external magnetic field is varied. This
commensurability scales with the channel shape and arrangement, although
screening effects play an important role. For large magnetic fields, some of
the vortices become pinned outside of the channels, leading to magnetic
hysteresis in the critical current. Some channel configurations also exhibit a
dynamical hysteresis in the flux-flow regime near the matching fields
Unconventional superconductors under rotating magnetic field II: thermal transport
We present a microscopic approach to the calculations of thermal conductivity
in unconventional superconductors for a wide range of temperatures and magnetic
fields. Our work employs the non-equilibrium Keldysh formulation of the
quasiclassical theory. We solve the transport equations using a variation of
the Brandt-Pesch-Tewordt (BPT) method, that accounts for the quasiparticle
scattering on vortices. We focus on the dependence of the thermal conductivity
on the direction of the field with the respect to the nodes of the order
parameter, and discuss it in the context of experiments aiming to determine the
shape of the gap from such anisotropy measurements. We consider quasi-two
dimensional Fermi surfaces with vertical line nodes and use our analysis to
establish the location of gap nodes in heavy fermion CeCoIn and organic
superconductor -(BEDT-TTF)Cu(NCS).Comment: 17 pages, 13 figure
Magnetoresistance of Granular Superconducting Metals in a Strong Magnetic Field
The magnetoresistance of a granular superconductor in a strong magnetic field
is considered. It is assumed that this field destroys the superconducting gap
in each grain, such that all interesting effects considered in the paper are
due to superconducting fluctuations. The conductance of the system is assumed
to be large, which allows us to neglect all localization effects as well as the
Coulomb interaction. It is shown that at low temperatures the superconducting
fluctuations reduce the one-particle density of states but do not contribute to
transport. As a result, the resistivity of the normal state exceeds the
classical resistivity approaching the latter only in the limit of extremely
strong magnetic fields, and this leads to a negative magnetoresistance. We
present detailed calculations of physical quatities relevant for describing the
effect and make a comparison with existing experiments.Comment: 24 pages, 10 figure
Random field spin models beyond one loop: a mechanism for decreasing the lower critical dimension
The functional RG for the random field and random anisotropy O(N)
sigma-models is studied to two loop. The ferromagnetic/disordered (F/D)
transition fixed point is found to next order in d=4+epsilon for N > N_c
(N_c=2.8347408 for random field, N_c=9.44121 for random anisotropy). For N <
N_c the lower critical dimension plunges below d=4: we find two fixed points,
one describing the quasi-ordered phase, the other is novel and describes the
F/D transition. The lower critical dimension can be obtained in an
(N_c-N)-expansion. The theory is also analyzed at large N and a glassy regime
is found.Comment: 4 pages, 5 figure
Asymmetric Fermi superfluid with different atomic species in a harmonic trap
We study the dilute fermion gas with pairing between two species and unequal
concentrations in a harmonic trap using the mean field theory and the local
density approximation. We found that the system can exhibit a superfluid shell
structure sandwiched by the normal fermions. This superfluid shell structure
occurs if the mass ratio is larger then certain critical value which increases
from the weak-coupling BCS region to the strong-coupling BEC side. In the
strong coupling BEC regime, the radii of superfluid phase are less sensitive to
the mass ratios and are similar to the case of pairing with equal masses.
However, the lighter leftover fermions are easier to mix with the superfluid
core than the heavier ones. A partially polarized superfluid can be found if
the majority fermions are lighter, whereas phase separation is still found if
they are heavier.Comment: 12 pages, 7 figure
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