4,380 research outputs found
Comment on "Phonon Spectrum and Dynamical Stability of a Dilute Quantum Degenerate Bose-Fermi Mixture
We show that the conclusions of a recent PRL by Pu et al is incorrect.Comment: late
Kinetics of the Phase Separation Transition in Cold-Atom Boson-Fermion Mixtures
We study the kinetics of the first order phase separation transition in
boson-fermion cold-atom mixtures. At sufficiently low temperatures such a
transition is driven by quantum fluctuations responsible for the formation of
critical nuclei of a stable phase. Based on a microscopic description of
interacting boson-fermion mixtures we derive an effective action for the
critical droplet and obtain an asymptotic expression for the nucleation rate in
the vicinity of the phase transition and near the spinodal instability of the
mixed phase. We also discuss effects of dissipation which play a dominant role
close to the transition point, and identify the regimes where quantum
nucleation can be experimentally observed in cold-atom systems.Comment: 4 pages 1 figure, typos correcte
Surface-atom force out of thermal equilibrium and its effect on ultra-cold atoms
The surface-atom Casimir-Polder-Lifshitz force out of thermal equilibrium is
investigated in the framework of macroscopic electrodynamics. Particular
attention is devoted to its large distance limit that shows a new, stronger
behaviour with respect to the equilibrium case. The frequency shift produced by
the surface-atom force on the the center-of-mass oscillations of a harmonically
trapped Bose-Einstein condensate and on the Bloch oscillations of an ultra-cold
fermionic gas in an optical lattice are discussed for configurations out of
thermal equilibrium.Comment: Submitted to JPA Special Issue QFEXT'0
Homoclinic orbits and chaos in a pair of parametrically-driven coupled nonlinear resonators
We study the dynamics of a pair of parametrically-driven coupled nonlinear
mechanical resonators of the kind that is typically encountered in applications
involving microelectromechanical and nanoelectromechanical systems (MEMS &
NEMS). We take advantage of the weak damping that characterizes these systems
to perform a multiple-scales analysis and obtain amplitude equations,
describing the slow dynamics of the system. This picture allows us to expose
the existence of homoclinic orbits in the dynamics of the integrable part of
the slow equations of motion. Using a version of the high-dimensional Melnikov
approach, developed by Kovacic and Wiggins [Physica D, 57, 185 (1992)], we are
able to obtain explicit parameter values for which these orbits persist in the
full system, consisting of both Hamiltonian and non-Hamiltonian perturbations,
to form so-called Shilnikov orbits, indicating a loss of integrability and the
existence of chaos. Our analytical calculations of Shilnikov orbits are
confirmed numerically
Lifshitz transitions in a heavy-Fermion liquid driven by short-range antiferromagnetic correlations in the two-dimensional Kondo lattice model
The heavy-Fermion liquid with short-range antiferromagnetic correlations is
carefully considered in the two-dimensional Kondo-Heisenberg lattice model. As
the ratio of the local Heisenberg superexchange to the Kondo coupling
increases, Lifshitz transitions are anticipated, where the topology of
the Fermi surface (FS) of the heavy quasiparticles changes from a hole-like
circle to four kidney-like pockets centered around . In-between
these two limiting cases, a first-order quantum phase transition is identified
at where a small circle begins to emerge within the large
deformed circle. When , the two deformed circles intersect
each other and then decompose into four kidney-like Fermi pockets via a
second-order quantum phase transition. As increases further, the
Fermi pockets are shifted along the direction () to (),
and the resulting FS is consistent with the FS obtained recently using the
quantum Monte Carlo cluster approach to the Kondo lattice system in the
presence of the antiferrmagnetic order.Comment: 4 pages, 5 figure
Electronic energy spectra and wave functions on the square Fibonacci tiling
We study the electronic energy spectra and wave functions on the square
Fibonacci tiling, using an off-diagonal tight-binding model, in order to
determine the exact nature of the transitions between different spectral
behaviors, as well as the scaling of the total bandwidth as it becomes finite.
The macroscopic degeneracy of certain energy values in the spectrum is invoked
as a possible mechanism for the emergence of extended electronic Bloch wave
functions as the dimension changes from one to two
Application of the Lifshitz theory to poor conductors
The Lifshitz formula for the dispersive forces is generalized to the
materials, which cannot be described with the local dielectric response.
Principal nonlocality of poor conductors is related with the finite screening
length of the penetrating field and the collisional relaxation; at low
temperatures the role of collisions plays the Landau damping. The spatial
dispersion makes the theory self consistent. Our predictions are compared with
the recent experiment. It is demonstrated that at low temperatures the
Casimir-Lifshitz entropy disappears as in the case of degenerate plasma and
as for the nondegenerate one.Comment: Accepted for publication in PR
Fermi Surface Reconstruction by Dynamic Magnetic Fluctuations
We demonstrate that nearly critical quantum magnetic fluctuations in strongly
correlated electron systems can change the Fermi surface topology and also lead
to spin charge separation (SCS) in two dimensions. To demonstrate these effects
we consider a small number of holes injected into the bilayer antiferromagnet.
The system has a quantum critical point (QCP) which separates magnetically
ordered and disordered phases. We demonstrate that in the physically
interesting regime there is a magnetically driven Lifshitz point (LP) inside
the magnetically disordered phase. At the LP the topology of the hole Fermi
surface is changed. We also demonstrate that in this regime the hole spin and
charge necessarily separate when approaching the QCP. The considered model
sheds light on generic problems concerning the physics of the cuprates.Comment: updated version, accepted to PR
Vacuum force on an atom in a magnetodielectric cavity
We demonstrate that, according to a recently suggested Lorentz-force approach
to the Casimir effect, the vacuum force on an atom embedded in a material
cavity differs substantially from the force on an atom of the cavity medium.
The force on an embedded atom is of the familiar (van der Waals and
Casimir-Polder) type, however, more strongly modified by the cavity medium than
usually considered. The force on an atom of the cavity medium is of the
medium-assisted force type with rather unusual properties, as demonstrated very
recently [M. S. Tomas, Phys. Rev. A 71, 060101(R) (2005)]. This implies similar
properties of the vacuum force between two atoms in a medium.Comment: RevTeX 4, 4 pages, 1 eps figure, corrected and slightly revise
General theory of electromagnetic fluctuations near a homogeneous surface, in terms of its reflection amplitudes
We derive new general expressions for the fluctuating electromagnetic field
outside a homogeneous material surface. The analysis is based on general
results from the thermodynamics of irreversible processes, and requires no
consideration of the material interior, as it only uses knowledge of the
reflection amplitudes for its surface. Therefore, our results are valid for all
homogeneous surfaces, including layered systems and metamaterials, at all
temperatures. In particular, we obtain new formulae for the near-field region,
which are important for interpreting the numerous current experiments probing
proximity effects for macroscopic and/or microscopic bodies separated by small
empty gaps. By use of Onsager's reciprocity relations, we obtain also the
general symmetry properties that must be satisfied by the reflection matrix of
any material.Comment: 5 page
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