5,949 research outputs found
Identifying the ejected population from disintegrating multiple systems
Kinematic studies of the Hipparcos catalogue have revealed associations that
are best explained as disintegrating multiple systems, presumably resulting
from a dynamical encounter between single/multiple systems in the field (Li et
al. 2009). In this work we explore the possibility that known ultra-cool dwarfs
may be components of disintegrating multiple systems, and consider the
implications for the properties of these objects. We will present here the
methods/techniques that can be used to search for and identify disintegrating
benchmark systems in three database/catalogues: Dwarf Archive, the Hipparcos
Main Catalogue, and the Gliese-Jahrei{\ss} Catalogue. Placing distance
constraints on objects with parallax or colour-magnitude information from
spectrophotometry allowed us to identify common distance associations. Proper
motion measurements allowed us to separate common proper motion multiples from
our sample of disintegrating candidates. Moreover, proper motion and positional
information allowed us to select candidate systems based on relative component
positions that were tracked back and projected forward through time. Using this
method we identified one candidate disintegrating quadruple association, and
two candidate disintegrating binaries, all of them containing one ultra-cool
dwarf.Comment: 5 pages, 1 figure, proceeding of The 19th Cambridge Workshop on Cool
Stars, Stellar Systems, and the Su
Magnetic Field Effect on the Supercurrent of an SNS junction
In this paper we study the effect of a Zeeman field on the supercurrent of a
mesoscopic SNS junction. It is shown that the supercurrent suppression is due
to a redistribution of current-carrying states in energy space. A dramatic
consequence is that (part of the) the suppressed supercurrent can be recovered
with a suitable non-equilibrium distribution of quasiparticles.Comment: 4 figures in postscrip
Superfluid stability in BEC-BCS crossover
We consider a dilute atomic gas of two species of fermions with unequal
concentrations under a Feshbach resonance. We find that the system can have
distinct properties due to the unbound fermions. The uniform state is stable
only when either (a) beyond a critical coupling strength, where it is a gapless
superfluid, or (b) when the coupling strength is sufficiently weak, where it is
a normal Fermi gas mixture. Phase transition(s) must therefore occur when the
resonance is crossed.Comment: 4 pages, 4 figure
Larkin-Ovchinnikov state in resonant Fermi gas
We construct the phase diagram of a homogeneous two component Fermi gas with
population imbalance under a Feshbach resonance. In particular, we study the
physics and stability of the Larkin-Ovchinnikov phase. We show that this phase
is stable over a much larger parameter range than what has been previously
reported by other authors.Comment: Typos correcte
Energy Resolved Supercurrent between two superconductors
In this paper I study the energy resolved supercurrent of a junction
consisting of a dirty normal metal between two superconductors. I also consider
a cross geometry with two additional arms connecting the above mentioned
junction with two normal reservoirs at equal and opposite voltages. The
dependence of the supercurrent between the two superconductors on the applied
voltages is studied.Comment: revtex, 7 pages, 8 figures. accepted by Phys. Rev.
Stationary Josephson effect in a weak-link between nonunitary triplet superconductors
A stationary Josephson effect in a weak-link between misorientated nonunitary
triplet superconductors is investigated theoretically. The non-self-consistent
quasiclassical Eilenberger equation for this system has been solved
analytically. As an application of this analytical calculation, the
current-phase diagrams are plotted for the junction between two nonunitary
bipolar wave superconducting banks. A spontaneous current parallel to the
interface between superconductors has been observed. Also, the effect of
misorientation between crystals on the Josephson and spontaneous currents is
studied. Such experimental investigations of the current-phase diagrams can be
used to test the pairing symmetry in the above-mentioned superconductors.Comment: 6 pages and 6 figure
Theory of Nonlinear Meissner Effect in High-Tc Superconductors
We investigate the nonlinear Meissner effect microscopically. Previous
studies did not consider a certain type of interaction effect on the nonlinear
phenomena. The scattering amplitude barely appears without being renormalized
into the Fermi-liquid parameter. With this effect we can solve the outstanding
issues (the quantitative problem, the temperature and angle dependences). The
quantitative calculation is performed with use of the fluctuation-exchange
approximation on the Hubbard model. It is also shown that the perturbation
expansion on the supercurrent by the vector potential converges owing to the
nonlocal effect
Andreev bound states and -junction transition in a superconductor / quantum-dot / superconductor system
We study Andreev bound states and -junction transition in a
superconductor / quantum-dot / superconductor (S-QD-S) system by Green function
method. We derive an equation to describe the Andreev bound states in S-QD-S
system, and provide a unified understanding of the -junction transition
caused by three different mechanisms: (1) {\it Zeeman splitting.} For QD with
two spin levels and , we find that the surface
of the Josephson current vs the configuration of
exhibits interesting profile: a sharp peak
around ; a positive ridge in the region of
; and a {\em % negative}, flat, shallow
plain in the region of . (2){\it \
Intra-dot interaction.} We deal with the intra-dot Coulomb interaction by
Hartree-Fock approximation, and find that the system behaves as a -junction when QD becomes a magnetic dot due to the interaction. The
conditions for -junction transition are also discussed. (3) {\it \
Non-equilibrium distribution.} We replace the Fermi distribution by
a non-equilibrium one , and allow
Zeeman splitting in QD where The curves of
vs show the novel effect of interplay of
non-equilibrium distribution with magnetization in QD.Comment: 18 pages, 8 figures, Late
Theory of the Transition at 0.2 K in Ni-doped Bi2Sr2CaCu2O8
A theory is put forward that the electronic phase transition at 0.2 K in
Ni-doped BiSrCaCuO is result of the formation of a spin
density wave in the system of Ni impurities. The driving force for the
transition is the exchange interaction between the impurity spins and the spins
of the conduction electrons. This creates a small gap at two of the four nodes
of the superconducting gap. The effect is to reduce the thermal conductivity by
a factor of two, as observed.Comment: 10 pages and 1 figur
Fragmented and Single Condensate Ground States of Spin-1 Bose Gas
We show that the ground state of a spin-1 Bose gas with an antiferro-
magnetic interaction is a fragmented condensate in uniform magnetic fields. The
number fluctuations in each spin component change rapidly from being enormous
(order ) to exceedingly small (order 1) as the magnetization of the system
increases. A fragmented condensate can be turned into a single condensate state
by magnetic field gradients. The conditions for existence and the method of
detecting fragmented states are presented.Comment: 4 pages, no figure
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