118 research outputs found
Bogoliubov-de Gennes study of trapped spin-imbalanced unitary Fermi gases
It is quite common that several different phases exist simultaneously in a
system of trapped quantum gases of ultra-cold atoms. One such example is the
strongly-interacting Fermi gas with two imbalanced spin species, which has
received a great amount of attention due to the possible presence of exotic
superfluid phases. By employing novel numerical techniques and algorithms, we
self-consistently solve the Bogoliubov de-Gennes equations, which describe
Fermi superfluids in the mean-field framework. From this study, we investigate
the novel phases of spin-imbalanced Fermi gases and examine the validity of the
local density approximation (LDA), which is often invoked in the extraction of
bulk properties from experimental measurements within trapped systems. We show
how the validity of the LDA is affected by the trapping geometry, number of
atoms and spin imbalance.Comment: 15 pages, 5 figures, to be published in New J. Phys. (focus issue on
"Strongly Correlated Quantum Fluids: From Ultracold Quantum Gases to QCD
Plasmas"
Optimization of the design of superconducting inhomogeneous nanowires
We study optimization of superconducting properties of inhomogeneous
nanowires. The main goal of this research is to find an optimized geometry that
allows one to maximize the desired property of superconductors, such as the
maximum value of local superconducting gap or total condensation energy. We
consider axially symmetric design of multi-layered nanowires with possibility
to adjust and change the layers thickness. We use numerical solution of the
Bogoliubov-de Gennes equations to obtain the local superconducting gap for
different arrangements of the inhomogeneous structures. The value of the
optimized properties can be up to 300% greater compared to a non-optimized
geometry. The optimized configuration of multilayers strongly depends on the
desired property one wants to optimize and on the number of layers in the
nanowire.Comment: Published in J. Phys.: Condens. Matter 20, 195204 (2008
Nambu-Jona Lasinio and Nonlinear Sigma Models in Condensed Matter Systems
We review various connections between condensed matter systems with the
Nambu-Jona Lasinio model and nonlinear sigma models. The field theoretical
description of interacting systems offers a systematic framework to describe
the dynamical generation of condensates. Resent findings of a duality between
the Nambu-Jona Lasinio model and the nonlinear sigma model enables us to
investigate various properties underlying both theories. In this review we
mainly focus on inhomogeneous condensations in static situations. The various
methods developed in the Nambu-Jona Lasinio model reveal the inhomogeneous
phase structures and also yield new inhomogeneous solutions in the nonlinear
sigma model owing to the duality. The recent progress on interacting systems in
finite systems is also reviewed.Comment: 24pages, 10 figures, Invited review paper commissioned by Symmetry.
Comments warmly welcom
Quantum Gross-Pitaevskii Equation
We introduce a non-commutative generalization of the Gross-Pitaevskii
equation for one-dimensional quantum gasses and quantum liquids. This
generalization is obtained by applying the time-dependent variational principle
to the variational manifold of continuous matrix product states. This allows
for a full quantum description of many body system ---including entanglement
and correlations--- and thus extends significantly beyond the usual mean-field
description of the Gross-Pitaevskii equation, which is known to fail for
(quasi) one-dimensional systems. By linearizing around a stationary solution,
we furthermore derive an associated generalization of the Bogoliubov -- de
Gennes equations. This framework is applied to compute the steady state
response amplitude to a periodic perturbation of the potential.Comment: 4.{\epsilon} pages + references and 4 pages supplementary material
(small revisions + extended discussion of periodic potential example
Generalized Second-Order Thomas-Fermi Method for Superfluid Fermi Systems
Using the -expansion of the Green's function of the
Hartree-Fock-Bogoliubov equation, we extend the second-order Thomas-Fermi
approximation to generalized superfluid Fermi systems by including the
density-dependent effective mass and the spin-orbit potential. We first
implement and examine the full correction terms over different energy intervals
of the quasiparticle spectra in calculations of finite nuclei. Final
applications of this generalized Thomas-Fermi method are intended for various
inhomogeneous superfluid Fermi systems.Comment: 8 pages, 10 figures, PR
Composite Topological Excitations in Ferromagnet-Superconductor Heterostructures
We investigate the formation of a new type of composite topological
excitation -- the skyrmion-vortex pair (SVP) -- in hybrid systems consisting of
coupled ferromagnetic and superconducting layers. Spin-orbit interaction in the
superconductor mediates a magnetoelectric coupling between the vortex and the
skyrmion, with a sign (attractive or repulsive) that depends on the topological
indices of the constituents. We determine the conditions under which a bound
SVP is formed, and characterize the range and depth of the effective binding
potential through analytical estimates and numerical simulations. Furthermore,
we develop a semiclassical description of the coupled skyrmion-vortex dynamics
and discuss how SVPs can be controlled by applied spin currents.Comment: Final version accepted by Physical Review Letters; 9 pages, 5 figure
Proximity effects at ferromagnet-superconductor interfaces
We study proximity effects at ferromagnet superconductor interfaces by
self-consistent numerical solution of the Bogoliubov-de Gennes equations for
the continuum, without any approximations. Our procedures allow us to study
systems with long superconducting coherence lengths. We obtain results for the
pair potential, the pair amplitude, and the local density of states. We use
these results to extract the relevant proximity lengths. We find that the
superconducting correlations in the ferromagnet exhibit a damped oscillatory
behavior that is reflected in both the pair amplitude and the local density of
states. The characteristic length scale of these oscillations is approximately
inversely proportional to the exchange field, and is independent of the
superconducting coherence length in the range studied. We find the
superconducting coherence length to be nearly independent of the ferromagnetic
polarization.Comment: 13 Pages total. Compressed .eps figs might display poorly, but will
print fin
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