126 research outputs found
Critical wetting, first-order wetting and prewetting phase transitions in binary mixtures of Bose-Einstein condensates
An ultralow-temperature binary mixture of Bose-Einstein condensates adsorbed
at an optical wall can undergo a wetting phase transition in which one of the
species excludes the other from contact with the wall. Interestingly, while
hard-wall boundary conditions entail the wetting transition to be of first
order, using Gross-Pitaevskii theory we show that first-order wetting as well
as critical wetting can occur when a realistic exponential optical wall
potential (evanescent wave) with a finite turn-on length is assumed.
The relevant surface excess energies are computed in an expansion in
, where is the healing length of condensate .
Experimentally, the wetting transition may best be approached by varying the
interspecies scattering length using Feshbach resonances. In the
hard-wall limit, , exact results are derived for the
prewetting and first-order wetting phase boundaries.Comment: 18 pages, 15 figure
Collective Excitations of Harmonically Trapped Ideal Gases
We theoretically study the collective excitations of an ideal gas confined in
an isotropic harmonic trap. We give an exact solution to the Boltzmann-Vlasov
equation; as expected for a single-component system, the associated mode
frequencies are integer multiples of the trapping frequency. We show that the
expressions found by the scaling ansatz method are a special case of our
solution. Our findings, however, are most useful in case the trap contains more
than one phase: we demonstrate how to obtain the oscillation frequencies in
case an interface is present between the ideal gas and a different phase.Comment: 4 pages, submitted to special issue of Eur. Phys. J. B "Novel Quantum
Phases and Mesoscopic Physics in Quantum Gases
Normal-Superfluid Interface for Polarized Fermion Gases
Recent experiments on imbalanced fermion gases have proved the existence of a
sharp interface between a superfluid and a normal phase. We show that, at the
lowest experimental temperatures, a temperature difference between N and SF
phase can appear as a consequence of the blocking of energy transfer across the
interface. Such blocking is a consequence of the existence of a SF gap, which
causes low-energy normal particles to be reflected from the N-SF interface. Our
quantitative analysis is based on the Hartree-Fock-Bogoliubov-de Gennes
formalism, which allows us to give analytical expressions for the thermodynamic
properties and characterize the possible interface scattering regimes,
including the case of unequal masses. Our central result is that the thermal
conductivity is exponentially small at the lowest experimental temperatures.Comment: 11 pages, 5 figure
Static interfacial properties of Bose-Einstein condensate mixtures
Interfacial profiles and interfacial tensions of phase-separated binary
mixtures of Bose-Einstein condensates are studied theoretically. The two
condensates are characterized by their respective healing lengths and
and by the inter-species repulsive interaction . An exact solution
to the Gross-Pitaevskii (GP) equations is obtained for the special case
and . Furthermore, applying a double-parabola
approximation (DPA) to the energy density featured in GP theory allows us to
define a DPA model, which is much simpler to handle than GP theory but
nevertheless still captures the main physics. In particular, a compact analytic
expression for the interfacial tension is derived that is useful for all
and . An application to wetting phenomena is presented for
condensates adsorbed at an optical wall. The wetting phase boundary obtained
within the DPA model nearly coincides with the exact one in GP theory.Comment: 24 pages, 6 figure
Criterion for explosive percolation transitions on complex networks
In a recent Letter, Friedman and Landsberg discussed the underlying mechanism
of explosive phase transitions on complex networks [Phys. Rev. Lett. 103,
255701 (2009)]. This Brief Report presents a modest, though more insightful
extension of their arguments. We discuss the implications of their results on
the cluster-size distribution and deduce that, under general conditions, the
percolation transition will be explosive if the mean number of nodes per
cluster diverges in the thermodynamic limit and prior to the transition
threshold. In other words, if, upon increase of the network size n the amount
of clusters in the network does not grow proportionally to n, the percolation
transition is explosive. Simulations and analytical calculations on various
models support our findings
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