69,281 research outputs found
Correlated hopping of bosonic atoms induced by optical lattices
In this work we analyze a particular setup with ultracold atoms trapped in
state-dependent lattices. We show that any asymmetry in the contact interaction
translates into one of two classes of correlated hopping. After deriving the
effective lattice Hamiltonian for the atoms, we obtain analytically and
numerically the different phases and quantum phase transitions. We find for
weak correlated hopping both Mott insulators and charge density waves, while
for stronger correlated hopping the system transitions into a pair superfluid.
We demonstrate that this phase exists for a wide range of interaction
asymmetries and has interesting correlation properties that differentiate it
from an ordinary atomic Bose-Einstein condensate.Comment: 24 pages with 9 figures, to appear in New Journal of Physic
Classical singularities and Semi-Poisson statistics in quantum chaos and disordered systems
We investigate a 1D disordered Hamiltonian with a non analytical step-like
dispersion relation whose level statistics is exactly described by Semi-Poisson
statistics(SP). It is shown that this result is robust, namely, does not depend
neither on the microscopic details of the potential nor on a magnetic flux but
only on the type of non-analyticity. We also argue that a deterministic kicked
rotator with a non-analytical step-like potential has the same spectral
properties. Semi-Poisson statistics (SP), typical of pseudo-integrable
billiards, has been frequently claimed to describe critical statistics, namely,
the level statistics of a disordered system at the Anderson transition (AT).
However we provide convincing evidence they are indeed different: each of them
has its origin in a different type of classical singularities.Comment: typos corrected, 4 pages, 3 figure
Equivalence of Faddeev-Jackiw and Dirac approaches for gauge theories
The equivalence between the Dirac method and Faddeev-Jackiw analysis for
gauge theories is proved. In particular we trace out, in a stage by stage
procedure, the standard classification of first and second class constraints of
Dirac's method in the F-J approach. We also find that the Darboux
transformation implied in the F-J reduction process can be viewed as a
canonical transformation in Dirac approach. Unlike Dirac's method the F-J
analysis is a classical reduction procedure, then the quantization can be
achieved only in the framework of reduce and then quantize approach with all
the know problems that this type of procedures presents. Finally we illustrate
the equivalence by means of a particular example.Comment: Latex v2.09, 15 pages, to appear in Int. J. Mod. Phys.
Non-equilibrium transport response from equilibrium transport theory
We propose a simple scheme that describes accurately essential
non-equilibrium effects in nanoscale electronics devices using equilibrium
transport theory. The scheme, which is based on the alignment and dealignment
of the junction molecular orbitals with the shifted Fermi levels of the
electrodes, simplifies drastically the calculation of current-voltage
characteristics compared to typical non-equilibrium algorithms. We probe that
the scheme captures a number of non-trivial transport phenomena such as the
negative differential resistance and rectification effects. It applies to those
atomic-scale junctions whose relevant states for transport are spatially placed
on the contact atoms or near the electrodes.Comment: 5 pages, 4 figures. Accepted in Physical Review
State selection in the noisy stabilized Kuramoto-Sivashinsky equation
In this work, we study the 1D stabilized Kuramoto Sivashinsky equation with
additive uncorrelated stochastic noise. The Eckhaus stable band of the
deterministic equation collapses to a narrow region near the center of the
band. This is consistent with the behavior of the phase diffusion constants of
these states. Some connections to the phenomenon of state selection in driven
out of equilibrium systems are made.Comment: 8 pages, In version 3 we corrected minor/typo error
Structure and electronic properties of molybdenum monoatomic wires encapsulated in carbon nanotubes
Monoatomic chains of molybdenum encapsulated in single walled carbon
nanotubes of different chiralities are investigated using density functional
theory. We determine the optimal size of the carbon nanotube for encapsulating
a single atomic wire, as well as the most stable atomic arrangement adopted by
the wire. We also study the transport properties in the ballistic regime by
computing the transmission coefficients and tracing them back to electronic
conduction channels of the wire and the host. We predict that carbon nanotubes
of appropriate radii encapsulating a Mo wire have metallic behavior, even if
both the nanotube and the wire are insulators. Therefore, encapsulating Mo
wires in CNT is a way to create conductive quasi one-dimensional hybrid
nanostructures.Comment: 8 pages, 10 figure
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