1,909 research outputs found
Reply to comment ``On the test of the modified BCS at finite temperature''
This is our formal Reply to revised version (v2) of arXiv: nucl-th/0510004v2.Comment: accepted in Physical Review
Quantum Size Effect in Conductivity of Multilayer Metal Films
Conductivity of quantized multilayer metal films is analyzed with an emphasis
on scattering by rough interlayer interfaces. Three different types of quantum
size effect (QSE) in conductivity are predicted. Two of these QSE are similar
to those in films with scattering by rough walls. The third type of QSE is
unique and is observed only for certain positions of the interface. The
corresponding peaks in conductivity are very narrow and high with a finite
cutoff which is due only to some other scattering mechanism or the smearing of
the interface. There are two classes of these geometric resonances. Some of the
resonance positions of the interface are universal and do not depend on the
strength of the interface potential while the others are sensitive to this
potential. This geometric QSE gradually disappears with an increase in the
width of the interlayer potential barrier.Comment: 12 pages, 10 figures, RevTeX4, to be published in Phys. Rev B (April
2003
Test of modified BCS model at finite temperature
A recently suggested modified BCS (MBCS) model has been studied at finite
temperature. We show that this approach does not allow the existence of the
normal (non-superfluid) phase at any finite temperature. Other MBCS predictions
such as a negative pairing gap, pairing induced by heating in closed-shell
nuclei, and ``superfluid -- super-superfluid'' phase transition are discussed
also. The MBCS model is tested by comparing with exact solutions for the picket
fence model. Here, severe violation of the internal symmetry of the problem is
detected. The MBCS equations are found to be inconsistent. The limit of the
MBCS applicability has been determined to be far below the ``superfluid --
normal'' phase transition of the conventional FT-BCS, where the model performs
worse than the FT-BCS.Comment: 8 pages, 9 figures, to appear in PR
ac-driven atomic quantum motor
We invent an ac-driven quantum motor consisting of two different, interacting
ultracold atoms placed into a ring-shaped optical lattice and submerged in a
pulsating magnetic field. While the first atom carries a current, the second
one serves as a quantum starter. For fixed zero-momentum initial conditions the
asymptotic carrier velocity converges to a unique non-zero value. We also
demonstrate that this quantum motor performs work against a constant load.Comment: 4 pages, 4 figure
Two-Dimensional Dynamics of Ultracold Atoms in Optical Lattices
We analyze the dynamics of ultracold atoms in optical lattices induced by a
sudden shift of the underlying harmonic trapping potential. In order to study
the effect of strong interactions, dimensionality and lattice topology on
transport properties, we consider bosonic atoms with arbitrarily strong
repulsive interactions, on a two-dimensional square lattice and a hexagonal
lattice. On the square lattice we find insulating behavior for weakly
interacting atoms and slow relaxation for strong interactions, even when a Mott
plateau is present, which in one dimension blocks the dynamics. On the
hexagonal lattice the center of mass relaxes to the new equilibrium for any
interaction strength.Comment: 4 pages, 6 figures; references added; improved figure
Can We Apply Statistical Laws to Small Systems? the Cerium Atom
It is shown that statistical mechanics is applicable to quantum systems with
finite numbers of particles, such as complex atoms, atomic clusters, etc.,
where the residual two-body interaction is sufficiently strong. This
interaction mixes the unperturbed shell-model basis states and produces
``chaotic'' many-body eigenstates. As a result, an interaction-induced
equilibrium emerges in the system, and temperature can be introduced. However,
the interaction between the particles and their finite number can lead to
prominent deviations of the equilibrium occupation numbers distribution from
the Fermi-Dirac shape. For example, this takes place in the cerium atom with
four valence electrons, which was used to compare the theory with realistic
numerical calculations.Comment: 4 pages, Latex, two figures in eps-forma
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