575 research outputs found
Effect of Weak Disorder on the BCS-BEC crossover in a two-dimensional Fermi Gas
In this article we study the two-dimensional (2D) ultracold Fermi gas with
weak impurity in the framework of mean-field theory where the impurity is
introduced through Gaussian fluctuations. We have investigated the role of the
impurity by studying the experimentally accessible quantities such as
condensate fraction and equation of state of the ultracold systems. Our
analysis reveals that, at the crossover the disorder enhances superfluidity,
which we attribute to the unique nature of the unitary region and to the
dimensional effect.Comment: To appear in Int. J. Mod. Phys.
Energy-transfer rate in a double-quantum-well system due to Coulomb coupling
We study the energy-transfer rate for electrons in a double-quantum-well
structure, where the layers are coupled through screened Coulomb interactions.
The energy-transfer rate between the layers (similar to the Coulomb drag effect
in which the momentum transfer rate is considered) is calculated as functions
of electron densities, interlayer spacing, the temperature difference of the
2DEGs, and the electron drift velocity in the drive layer. We employ the full
wave vector and frequency dependent random-phase approximation at finite
temperature to describe the effective interlayer Coulomb interaction. We find
that the collective modes (plasmons) of the system play a dominant role in the
energy transfer rates. The contribution of optical phonons to the transfer
rates through the phonon mediated Coulomb coupling mechanism has also been
considered.Comment: LaTex, 5 pages, 4 figures, uses grafik.sty (included
Investigating Dirty Crossover through Fidelity Susceptibility and Density of States
We investigate the BCS-BEC crossover in an ultracold atomic gas in the
presence of disorder. The disorder is incorporated in the mean-field formalism
through Gaussian fluctuations. We observe evolution to an asymmetric line-shape
of fidelity susceptibility as a function of interaction coupling with
increasing disorder strength which may point to an impending quantum phase
transition. The asymmetric line-shape is further analyzed using the statistical
tools of skewness and kurtosis. We extend our analysis to density of states
(DOS) for a better understanding of the crossover in the disordered
environment.Comment: 12 pages, 6 figures. To appear in Int. J. Mod. Phys.
Controlled dephasing in single-dot Aharonov-Bohm interferometers
We study the Fano effect and the visibility of the Aharonov-Bohm oscillations
for a mesoscopic interferometer with an embedded quantum dot in the presence of
a nearby second dot. When the electron-electron interaction between the two
dots is considered the nearby dot acts as a charge detector. We compute the
currents through the interferometer and detector within the Keldysh formalism
and the self-energy of the non-equilibrium Green functions is found up to the
second order in the interaction strength. The current formula contains a
correction to the Landauer-B\"{uttiker} formula. Its contribution to transport
and dephasing is discussed. As the bias applied on the detector is increased,
the amplitude of both the Fano resonance and Aharonov-Bohm oscillations are
considerably reduced due to controlled dephasing. This result is explained by
analyzing the behavior of the imaginary part of the self-energy as a function
of energy and bias. We investigate as well the role of the ring-dot coupling.
Our theoretical results are consistent to the experimental observation of Buks
{\it et al.} [Nature {\bf 391}, 871 (1998)].Comment: 24 pages, 8 figure
Collective Modes in a Bilayer Dipolar Fermi Gas and the Dissipationless Drag Effect
Cataloged from PDF version of article.We consider the collective modes of a bilayer dipolar Fermi system in which the particles interact via long range (similar to 1/r (3)) interaction. Assuming that each layer has a background flow which varies little and that the dynamics of the superfluid near T=0 is the same as that of a normal fluid, we obtain the dispersion relations for the collective modes in the presence of background flow. Decomposing the background flow into two parts, the center-of-mass flow and counterflow, we focus on the properties of the counterflow. We first find an estimate of the change in the zero-point energy Delta E (ZP) due to counterflow for a unit area of bilayer. Combining this with the free energy F of the system and taking the partial derivatives with respect to background velocities in the layers, we determine the current densities which reveal the fact that current in one layer does not only depend on the velocity in the same layer but also on the velocity of the other layer. This is the drag effect and we calculate the drag coefficient
Energy transfer rate in Coulomb coupled quantum wires
Cataloged from PDF version of article.We study the energy transfer rate for electrons in two parallel quantum wires due to interwire Coulomb interactions. The energy transfer rate between the wires (similar to the Coulomb drag effect in which momentum transfer rate is measured) is calculated as a function of temperature for several wire separation distances. We employ the full wave vector and frequency dependent random-phase approximation at finite temperature to describe the effective interwire Coulomb interaction. We find that the energy transfer rate at intermediate temperatures (i.e., T similar to 0.3E(F)) is dominated by the collective modes (plasmons) of ale system. Nonlinear effects on the energy transfer rate is also explored. (C) 1997 American Institute of Physics
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