2,026 research outputs found
Coexistence of Bose condensation and pairing in Boson mixtures
We consider the problem when there are two kinds of Bosons with an attraction
between them. We find the system to consist of two Bose condensates with an
additional pairing order between the Bosons. The properties of this state are
discussed
Critical velocities and the effect of steady and oscillating rotations on solid He4
We apply our recently developed model of a Bose condensate of quantum kink
wave in solid He4 to understand recent torsional oscillator experimental
results of the citical velocities and the effect of the steady and oscillating
rotations at around 0.1 degree K. When the D.C. rotation is present we find a
decrease of the Q factor given by where is the superfluid fraction;
, the D. C. angular rotation velocity, , the torsional
oscillator oscillating frequency. We estimate the AC critical velocity
as that required to generate a kink wave of wavevector
where is the distance between nodes of the dislocation
network. We generalize this to include a steady rotation and find a D. C.
critical velocity .
Estimates for both the steady and the oscillating critical velocities are in
order of magnitude agreement with experimental results. We have also examined
an alternative mechanism of kink tunnelling through a node in the dislocation
networm and find that there is also a dependence on the torsional oscillator
frequency: The DC
critical velocity is ten times higher than the experimental
value
'Electron' and 'photon' emerging from supersymmetric neutral particles: A possible realization in ultracold Bose-Fermi atom mixture
We show that the 'electron' and 'photon' can emerge from a supersymmetric
Hubbard model which is a non-relativistic theory of the neutral particles. The
Higgs boson and 'photon' may not appear in the same phase of the phase diagram.
In a Mott insulator phase of the boson, the 'electron' and 'photon' are
stablized by an induced Coulomb interaction between 'electrons'. This emergent
mechanism may be 'realized' in an ultracold Bose-Fermi atom mixture except the
long range Coulomb interaction is repalced by a nearest neighbor one. We
suggest to create 'external electric field' so that the 'electron' excitation
can be observed by measuring the linear density-density response of the
'electron' gas to the 'external field' in the time flying experiment of the
mixture. The Fermi surface of the 'electron' gas may also be expected to be
observed in the time flying.Comment: 4 pages, 1 figur
Electron-like and photon-like excitations in an ultracold Bose-Fermi atom mixture
We show that the electron-like and photon-like excitations may exist in a
three-dimensional Bose-Fermi Hubbard model describing ultracold Bose-Fermi atom
mixtures in optical lattices. In a Mott insulating phase of the Bose atoms,
these excitations are stabilized by an induced repulsive interaction between
'electrons' if the Fermi atoms are nearly half filling. We suggest to create
'external electric field' so that the electron-like excitation can be observed
by measuring the linear density-density response of the 'electron' gas to the
'external field' in a time-of-flight experiment of the mixture. The Fermi
surface of the 'electron' gas may also be expected to be observed in the
time-of-flight.Comment: Supersede cond-mat/051033
Quantum Spinodal Decomposition in Multicomponent Bose-Einstein Condensates
We investigate analytically the non-equilibrium spatial phase segregation
process of a mixture of alkali Bose-Einstein condensates. Two stages (I and II)
are found in analogy to the classical spinodal decomposition.
The coupled non-linear Schr\"odinger equations enable us to give a
quantitative picture of the present dynamical process in a square well trap.
Both time and length scales in the stage I are obtained.
We further propose that the stage II is dominated by the Josephson effect
between different domains of same condensate different from scenarios in the
classical spinodal decomposition.
Its time scale is estimated.Comment: revte
Non conservation of the magnetization current across magnetic hetero-structures
We show that when the magnetizations on opposite sides of a junction are not
collinear, the magnetization current is not conserved as the junction is
crossed. Thus the usual treatment of this problem needs to be modified. We
argue that this is due to an implicit assumption of an external torque that is
required to clamp the magnetization in place. The physical consequence of this
is explored
Soliton and 2D domains in ultra-thin magnetic films
We show that many two dimensional domain patterns observed in Monte Carlo
simulations can be obtained from the many soliton solutions of the imaginary
time Sine Gordon equation. This opens the door to analytic physical
understanding of the micromagnetics in ultra-thin films.Comment: 9 pages, 3 PostScript figure
Internal dipolar field and soft magnons in periodic nanocomposite magnets
We study spin wave excitations in a three-dimensional nanocomposite magnet of
exchange coupled hard (SmCo) and soft (FeCo) phases. The dipolar
interaction splits the spin wave energies into the upper and lower branches of
the spin wave manifold. When the amount of the soft phase is increased the
energy of low-lying spin excitations is considerably softened due to two
reasons: (i) the low- lying mode locked into the soft phase region with a spin
wave gap at which scales approximately proportional to the
anisotropy constant of the soft phase and (ii) the internal dipolar field which
comes from magnetic charges forming at hard-soft boundaries with normals
parallel to the magnetization displaces the spin wave manifold toward the lower
energies. With adding more soft phase the spin wave gap closes and the system
moves to another ground state characterized by the magnetization mismatch
between spins of the hard and soft phases.Comment: 15 pages, 4 figure
Generalization of conformal mapping to scattering of electromagnetic waves from surfaces: An example of a triangle
We discuss a way to exploit the conformal mapping to study the response of a
finite metallic element of arbitrary shape to an external electromagnetic field
at finite frequencies. This provides a simple way to study different physics
issues and provides new insights that include the issue of vorticity and eddy
current, and the nature of the divergent electric field at the boundaries and
at corners. The nature of the resonance can be directly addressed and
clarified. We study an example of an equilateral triangle and found good
agreement with results obtained with traditional numerical techniques
Stable and unstable regimes in Bose-Fermi mixture with attraction between components
A collapse of the trapped boson- fermion mixture with the attraction between
bosons and fermions is investigated in the framework of the effective
Hamiltonian for the Bose system. The properties of the Rb and K
mixture are analyzed quantitatively at . We find numerically solutions of
modified Gross- Pitaevskii equation which continuously go from stable to
unstable branch. We discuss the relation of the onset of collapse with
macroscopic properties of the system. A comparison with the case of a Bose
condensate of atomic system is given.Comment: 7 pages, 5 figure
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