139,466 research outputs found
Topological Superfluid Phase of a Dipolar Fermi Gas in a 2D Optical Lattice
In a dipolar Fermi gas, the anisotropic interaction between electric dipoles
can be turned into an effectively attractive interaction in the presence of a
rotating electric field. We show that the topological superfluid
phase can be realized in a single-component dipolar Fermi gas trapped in a 2D
square optical lattice with this attractive interaction at low temperatures.
The superfluid state has potential applications for topological
quantum computing. We obtain the phase diagram of this system at zero
temperature. In the weak-coupling limit, the p-wave superfluid phase is stable
for all filling factors. As the interaction strength increases, it is stable
close to filling factors or , and phase separation takes place in
between. When the interaction strength is above a threshold, the system is
phase separated for any . The transition temperature of the
superfluid state is estimated and the implication for
experiments is discussed.Comment: 10 pages, 4 figure
Phase transition in site-diluted Josephson junction arrays: A numerical study
We numerically investigate the intriguing effects produced by random
percolative disorder in two-dimensional Josephson-junction arrays. By dynamic
scaling analysis, we evaluate critical temperatures and critical exponents with
high accuracy. It is observed that, with the introduction of site-diluted
disorder, the Kosterlitz-Thouless phase transition is eliminated and evolves
into a continuous transition with power-law divergent correlation length.
Moreover, genuine depinning transition and creep motion are studied, evidence
for distinct creep motion types is provided. Our results not only are in good
agreement with the recent experimental findings, but also shed some light on
the relevant phase transitions.Comment: 7 pages, 8 figures, Phys. Rev. B (in press
Multiple and virtual photon processes in radiation-induced magnetoresistance oscillations in two-dimensional electron systems
Recently discovered new structures and zero-resistance states outside the
well-known oscillations are demonstrated to arise from multiphoton assisted
processes, by a detailed analysis of microwave photoresistance in
two-dimensional electron systems under enhanced radiation. The concomitant
resistance dropping and peak narrowing observed in the experiments are also
reproduced. We show that the radiation-induced suppression of average
resistance comes from virtual photon effect and exists throughout the whole
magnetic field range.Comment: 4 pages, 2 figures, published versio
Nonsequential Double Ionization with Polarization-gated Pulses
We investigate laser-induced nonsequential double ionization by a
polarization-gated laser pulse, constructed employing two counter-rotating
circularly polarized few cycle pulses with a time delay . We address the
problem within a classical framework, and mimic the behavior of the
quantum-mechanical electronic wave packet by means of an ensemble of classical
electron trajectories. These trajectories are initially weighted with the
quasi-static tunneling rate, and with suitably chosen distributions for the
momentum components parallel and perpendicular to the laser-field polarization,
in the temporal region for which it is nearly linearly polarized. We show that,
if the time delay is of the order of the pulse length, the
electron-momentum distributions, as functions of the parallel momentum
components, are highly asymmetric and dependent on the carrier-envelope (CE)
phase. As this delay is decreased, this asymmetry gradually vanishes. We
explain this behavior in terms of the available phase space, the quasi-static
tunneling rate and the recollision rate for the first electron, for different
sets of trajectories. Our results show that polarization-gating technique may
provide an efficient way to study the NSDI dynamics in the single-cycle limit,
without employing few-cycle pulses.Comment: 17 pages, 6 figure
Magnetoresistance oscillations in two-dimensional electron systems under monochromatic and bichromatic radiations
The magnetoresistance oscillations in high-mobility two-dimensional electron
systems induced by two radiation fields of frequencies 31 GHz and 47 GHz, are
analyzed in a wide magnetic-field range down to 100 G, using the
balance-equation approach to magnetotransport for high-carrier-density systems.
The frequency mixing processes are shown to be important. The predicted peak
positions, relative heights, radiation-intensity dependence and their relation
with monochromatic resistivities are in good agreement with recent experimental
finding [M. A. Zudov {\it et al.} Phys. Rev. Lett. 96, 236804 (2006)].Comment: 4 pages, 3 figure
Multigrid solver for axisymmetrical 2D fluid equations
We have developed an efficient algorithm for steady axisymmetrical 2D fluid
equations. The algorithm employs multigrid method as well as standard implicit
discretization schemes for systems of partial differential equations. Linearity
of the multigrid method with respect to the number of grid points allowed us to
use grid, where we could achieve solutions in several minutes.
Time limitations due to nonlinearity of the system are partially avoided by
using multi level grids(the initial solution on grid was
extrapolated steady solution from grid which allowed using
"long" integration time steps). The fluid solver may be used as the basis for
hybrid codes for DC discharges.Comment: preliminary version; presented at 28 ICPIG, July 15-20, 2007, Prague,
Czech Republi
The finite-width Laplace sum rules for scalar glueball in instanton liquid model
In the framework of a semi-classical expansion for quantum chromodynamics in
the instanton liquid background, the correlation function of the
scalar glueball current is given. Besides the pure classical and quantum
contributions, the contributions arising from the interactions between the
classical instanton fields and quantum gluons are taken into account as well.
Instead of the usual zero-width approximation for the resonance, the
Brite-Wigner form for the spectral function of the finite-width resonance is
adopted. The family of the Laplace sum rules for the scalar glueball in quantum
chromodynamics with and without light quarks are studed. A consistency between
the subtracted and unsubtracted sum rules are very well justified, and the
values of the mass, decay width, and the coupling to the corresponding current
for the resonance in which the glueball fraction is dominant, are
obtained.Comment: 6 figure
Solutions to CDM Universe Derived from Global Brane Model
An exact solution of brane universe is studied and the result indicates that
Friedmann equations on the brane are modified with an extra term. This term can
play the role of dark energy and make the universe accelerate. In order to
derive the CDM Universe from this global brane model, the new
solutions are obtained to describe the manifold.Comment: 7 pages, no figure, accepted by MPL
Confinement induced resonances in anharmonic waveguides
We develop the theory of anharmonic confinement-induced resonances (ACIR).
These are caused by anharmonic excitation of the transverse motion of the
center of mass (COM) of two bound atoms in a waveguide. As the transverse
confinement becomes anisotropic, we find that the COM resonant solutions split
for a quasi-1D system, in agreement with recent experiments. This is not found
in harmonic confinement theories. A new resonance appears for repulsive
couplings () for a quasi-2D system, which is also not seen with
harmonic confinement. After inclusion of anharmonic energy corrections within
perturbation theory, we find that these ACIR resonances agree extremely well
with anomalous 1D and 2D confinement induced resonance positions observed in
recent experiments. Multiple even and odd order transverse ACIR resonances are
identified in experimental data, including up to N=4 transverse COM quantum
numbers.Comment: 16 pages,6 fugure
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