8,938 research outputs found
Synchronization in the BCS Pairing Dynamics as a Critical Phenomenon
Fermi gas with time-dependent pairing interaction hosts several different
dynamical states. Coupling between the collective BCS pairing mode and
individual Cooper pair states can make the latter either synchronize or
dephase. We describe transition from phase-locked undamped oscillations to
Landau-damped dephased oscillations in the collisionless, dissipationless
regime as a function of coupling strength. In the dephased regime, we find a
second transition at which the long-time asymptotic pairing amplitude vanishes.
Using a combination of numerical and analytical methods we establish a
continuous (type II) character of both transitions
On the ternary complex analysis and its applications
Previouly a possible extension of the complex number, together with its
connected trigonometry was introduced. In this paper we focuss on the simplest
case of ternary complex numbers. Then, some types of holomorphicity adapted to
the ternary complex numbers and the corresponding results upon integration of
differential forms are given. Several physical applications are given, and in
particuler one type of holomorphic function gives rise to a new form of
stationary magnetic field. The movement of a monopole type object in this field
is then studied and shown to be integrable. The monopole scattering in the
ternary field is finally studied.Comment: LaTeX 28 page
Cosmic Colored Black Holes
We present spherically symmetric static solutions (a particle-like solution
and a black hole solution) in the Einstein-Yang-Mills system with a
cosmological constant.Although their gravitational structures are locally
similar to those of the Bartnik-McKinnon particles or the colored black holes,
the asymptotic behavior becomes quite different because of the existence of a
cosmological horizon. We also discuss their stability by means of a catastrophe
theory as well as a linear perturbation analysis and find the number of
unstable modes.Comment: 12 pages, latex, 4 figures (available upon request
DMRG and the Two Dimensional t-J Model
We describe in detail the application of the recent non-Abelian Density
Matrix Renormalization Group (DMRG) algorithm to the two dimensional t-J model.
This extension of the DMRG algorithm allows us to keep the equivalent of twice
as many basis states as the conventional DMRG algorithm for the same amount of
computational effort, which permits a deeper understanding of the nature of the
ground state.Comment: 16 pages, 3 figures. Contributed to the 2nd International Summer
School on Strongly Correlated Systems, Debrecen, Hungary, Sept. 200
Spin and Charge Structure of the Surface States in Topological Insulators
We investigate the spin and charge densities of surface states of the
three-dimensional topological insulator , starting from the continuum
description of the material [Zhang {\em et al.}, Nat. Phys. 5, 438 (2009)]. The
spin structure on surfaces other than the 111 surface has additional complexity
because of a misalignment of the contributions coming from the two sublattices
of the crystal. For these surfaces we expect new features to be seen in the
spin-resolved ARPES experiments, caused by a non-helical spin-polarization of
electrons at the individual sublattices as well as by the interference of the
electron waves emitted coherently from two sublattices. We also show that the
position of the Dirac crossing in spectrum of surface states depends on the
orientation of the interface. This leads to contact potentials and surface
charge redistribution at edges between different facets of the crystal.Comment: Use the correct spin operator. Changes affect the surface states spin
structure, but not the spectru
Magneto-infrared modes in InAs-AlSb-GaSb coupled quantum wells
We have studied a series of InAs/GaSb coupled quantum wells using
magneto-infrared spectroscopy for high magnetic fields up to 33T within
temperatures ranging from 4K to 45K in both Faraday and tilted field
geometries. This type of coupled quantum wells consists of an electron layer in
the InAs quantum well and a hole layer in the GaSb quantum well, forming the
so-called two dimensional electron-hole bilayer system. Unlike the samples
studied in the past, the hybridization of the electron and hole subbands in our
samples is largely reduced by having narrower wells and an AlSb barrier layer
interposed between the InAs and the GaSb quantum wells, rendering them weakly
hybridized. Previous studies have revealed multiple absorption modes near the
electron cyclotron resonance of the InAs layer in moderately and strongly
hybridized samples, while only a single absorption mode was observed in the
weakly hybridized samples. We have observed a pair of absorption modes
occurring only at magnetic fields higher than 14T, which exhibited several
interesting phenomena. Among which we found two unique types of behavior that
distinguishes this work from the ones reported in the literature. This pair of
modes is very robust against rising thermal excitations and increasing magnetic
fields alligned parallel to the heterostructures. While the previous results
were aptly explained by the antilevel crossing gap due to the hybridization of
the electron and hole wavefunctions, i.e. conduction-valence Landau level
mixing, the unique features reported in this paper cannot be explained within
the same concept. The unusual properties found in this study and their
connection to the known models for InAs/GaSb heterostructures will be
disccused; in addition, several alternative ideas will be proposed in this
paper and it appears that a spontaneous phase separation can account for most
of the observed features
Characterizing asymptotically anti-de Sitter black holes with abundant stable gauge field hair
In the light of the "no-hair" conjecture, we revisit stable black holes in
su(N) Einstein-Yang-Mills theory with a negative cosmological constant. These
black holes are endowed with copious amounts of gauge field hair, and we
address the question of whether these black holes can be uniquely characterized
by their mass and a set of global non-Abelian charges defined far from the
black hole. For the su(3) case, we present numerical evidence that stable black
hole configurations are fixed by their mass and two non-Abelian charges. For
general N, we argue that the mass and N-1 non-Abelian charges are sufficient to
characterize large stable black holes, in keeping with the spirit of the
"no-hair" conjecture, at least in the limit of very large magnitude
cosmological constant and for a subspace containing stable black holes (and
possibly some unstable ones as well).Comment: 33 pages, 13 figures, minor change
Rapid ramps across the BEC-BCS crossover: a novel route to measuring the superfluid gap
We investigate the response of superfluid Fermi gases to rapid changes of the
three-dimensional s-wave scattering length a by solving the time-dependent
Bogoliubov-de Gennes equations. In general the magnitude of the order parameter
|\Delta| performs oscillations, which are sometimes called the "Higgs" mode,
with the angular frequency 2 \Delta_{gap}/ \hbar, where \Delta_{gap} is the gap
in the spectrum of fermionic excitations. Firstly, we excite the oscillations
with a linear ramp of 1/a and study the evolution of |\Delta|. Secondly, we
continously drive the system with a sinusoidal modulation of 1/a. In the first
case, the oscillations in |\Delta| damp according to a power law. In the second
case, the continued driving causes revivals in the oscillations. In both cases,
the excitation of the oscillations causes a reduction in the time-averaged
value of |\Delta|. We propose two experimental protocols, based around the two
approaches, to measure the frequency and damping of the oscillations, and hence
\Delta_{gap}.Comment: 7 pages, 7 figure
Peculiarities of dynamics of Dirac fermions associated with zero-mass lines
Zero-mass lines result in appearance of linear dispersion modes for Dirac
fermions. These modes play an important role in various physical systems.
However, a Dirac fermion may not precisely follow a single zero-mass line, due
to either tunneling between different lines or centrifugal forces. Being
shifted from a zero-mass line the Dirac fermion acquires mass which can
substantially influence its expected "massless" behavior. In the paper we
calculate the energy gap caused by the tunneling between two zero-mass lines
and show that its opening leads to the delocalization of linear dispersion
modes. The adiabatic bending of a zero-mass line gives rise to geometric
phases. These are the Berry phase, locally associated with a curvature, and a
new phase resulting from the mass square asymmetry in the vicinity of a
zero-mass line.Comment: 6 pages, 4 figures. In the second version some references were added
and minor changes were made in the introductio
Pion damping width from SU(2) x SU(2) NJL model
Within the framework of the NJL model, we investigate the modification of the
pion damping width in a hot pion gas for temperatures ranging from 0 to 180
MeV. The pion is found to broaden noticeably at T > 60 MeV. Near the chiral
phase transition T ~ 180 MeV, the pion width is saturated and amounts to 70
MeV. The main contribution to the width comes from pion-pion collisions. Other
contributions are found negligibly small.Comment: LaTeX2e, 13 pages, 2 figure
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