330 research outputs found
Observing Zitterbewegung for photons near the Dirac point of a two-dimensional photonic crystal
It is shown, for the first time, that the zitterbewegung of photon can appear
near the Dirac point in two-dimensional photonic crystal. The superiority of
such a phenomenon for photons is that it can be found in different scaling
structures with wide frequency regions. It can be observed by measuring the
time dependence of the transmission coefficient through photonic crystal slabs.
Thus, it is particularly suited for experimentally observing this effect. We
have observed such a phenomenon by exact numerical simulations, confirming a
long-standing theoretical prediction
Zitterbewegung (trembling motion) of electrons in narrow gap semiconductors
Theory of trembling motion [Zitterbewegung (ZB)] of charge carriers in
various narrow-gap materials is reviewed. Nearly free electrons in a periodic
potential, InSb-type semiconductors, bilayer graphene, monolayer graphene and
carbon nanotubes are considered. General features of ZB are emphasized. It is
shown that, when the charge carriers are prepared in the form of Gaussian wave
packets, the ZB has a transient character with the decay time of femtoseconds
in graphene and picoseconds in nanotubes. Zitterbewegung of electrons in
graphene in the presence of an external magnetic field is mentioned. A
similarity of ZB in semiconductors to that of relativistic electrons in a
vacuum is stressed. Possible ways of observing the trembling motion in solids
are mentioned.Comment: 8 pages, 5 figure
On the supercritically diffusive magneto-geostrophic equations
We address the well-posedness theory for the magento-geostrophic equation,
namely an active scalar equation in which the divergence-free drift velocity is
one derivative more singular than the active scalar. In the presence of
supercritical fractional diffusion given by (-\Delta)^\gamma, where 0<\gamma<1,
we discover that for \gamma>1/2 the equations are locally well-posed, while for
\gamma<1/2 they are ill-posed, in the sense that there is no Lipschitz solution
map. The main reason for the striking loss of regularity when \gamma goes below
1/2 is that the constitutive law used to obtain the velocity from the active
scalar is given by an unbounded Fourier multiplier which is both even and
anisotropic. Lastly, we note that the anisotropy of the constitutive law for
the velocity may be explored in order to obtain an improvement in the
regularity of the solutions when the initial data and the force have thin
Fourier support, i.e. they are supported on a plane in frequency space. In
particular, for such well-prepared data one may prove the local existence and
uniqueness of solutions for all values of \gamma \in (0,1).Comment: 24 page
CFHT AO Imaging of the CLASS Gravitational Lens System B1359+154
We present adaptive optics imaging of the CLASS gravitational lens system
B1359+154 obtained with the Canada-France-Hawaii Telescope (CFHT) in the
infrared K band. The observations show at least three brightness peaks within
the ring of lensed images, which we identify as emission from multiple lensing
galaxies. The results confirm the suspected compound nature of the lens, as
deduced from preliminary mass modeling. The detection of several additional
nearby galaxies suggests that B1359+154 is lensed by the compact core of a
small galaxy group. We attempted to produce an updated lens model based on the
CFHT observations and new 5-GHz radio data obtained with the MERLIN array, but
there are too few constraints to construct a realistic model at this time. The
uncertainties inherent with modeling compound lenses make B1359+154 a
challenging target for Hubble constant determination through the measurement of
differential time delays. However, time delays will offer additional
constraints to help pin down the mass model. This lens system therefore
presents a unique opportunity to directly measure the mass distribution of a
galaxy group at intermediate redshift.Comment: 12 pages including 3 figures; ApJL accepte
Cyclotron motion in graphene
We investigate cyclotron motion in graphene monolayers considering both the
full quantum dynamics and its semiclassical limit reached at high carrier
energies. Effects of zitterbewegung due to the two dispersion branches of the
spectrum dominate the irregular quantum motion at low energies and are obtained
as a systematic correction to the semiclassical case. Recent experiments are
shown to operate in the semiclassical regime.Comment: 6 pages, 1 figure include
Zitterbewegung of nearly-free and tightly bound electrons in solids
We show theoretically that nonrelativistic nearly-free electrons in solids
should experience a trembling motion
(Zitterbewegung, ZB) in absence of external fields, similarly to relativistic
electrons in vacuum.
The Zitterbewegung is directly related to the influence of periodic potential
on the free electron motion.
The frequency of ZB is , where is the energy
gap. The amplitude of ZB is determined by the strength of periodic potential
and the lattice period and it can be of the order of nanometers. We show that
the amplitude of ZB does not depend much on the width of the wave packet
representing an electron in real space.
An analogue of the Foldy-Wouthuysen transformation, known from relativistic
quantum mechanics, is introduced in order to decouple electron states in
various bands. We demonstrate that, after the bands are decoupled, electrons
should be treated as particles of a finite size.
In contrast to nearly-free electrons we consider a two-band model of tightly
bound electrons.
We show that also in this case the electrons should experience the trembling
motion. It is concluded that the phenomenon of Zitterbewegung of electrons in
crystalline solids is a rule rather than an exception.Comment: 22 pages, 6 figures Published version, minor changes mad
Golden gravitational lensing systems from the Sloan Lens ACS Survey. I. SDSS J1538+5817: one lens for two sources
We present a lensing and photometric study of the exceptional system SDSS
J1538+5817, identified by the SLACS survey. The lens is a luminous elliptical
at redshift z=0.143. Using HST public images in two different filters, the
presence of two background sources lensed into an Einstein ring and a double
system is ascertained. Our new spectroscopic observations, performed at the
NOT, reveal that the two sources are located at the same redshift z=0.531. We
investigate the total mass distribution of the lens between 1 and 4 kpc from
the galaxy center by means of parametric and non-parametric lensing codes that
describe the multiple images as point-like objects. Several disparate lensing
models agree on: (1) reproducing accurately the observed image positions; (2)
predicting a nearly axisymmetric total mass distribution, centered and oriented
as the light distribution; (3) measuring a value of 8.11 x 10^{10} M_{Sun} for
the total mass projected within the Einstein radius of 2.5 kpc; (4) estimating
a total mass density profile slightly steeper than an isothermal one. A fit of
the SDSS multicolor photometry with CSP models provides a value of 20 x 10^{10}
M_{Sun} for the total stellar mass of the galaxy and of 0.9 for the fraction of
projected luminous over total mass enclosed inside the Einstein radius. By
combining lensing and photometric mass measurements, we differentiate the lens
mass content in terms of luminous and dark matter components. This
two-component modeling, which is viable only in extraordinary systems like SDSS
J1538+5817, leads to a description of the global properties of the galaxy dark
matter halo. Extending these results to a larger number of lenses would improve
considerably our understanding of galaxy formation and evolution processes in
the LCDM scenario.Comment: 21 pages, 16 figures, accepted by The Astrophysical Journa
The Sloan Lens ACS Survey. IX. Colors, Lensing and Stellar Masses of Early-type Galaxies
We present the current photometric dataset for the Sloan Lens ACS (SLACS)
Survey, including HST photometry from ACS, WFPC2, and NICMOS. These data have
enabled the confirmation of an additional 15 grade `A' (certain) lens systems,
bringing the number of SLACS grade `A' lenses to 85; including 13 grade `B'
(likely) systems, SLACS has identified nearly 100 lenses and lens candidates.
Approximately 80% of the grade `A' systems have elliptical morphologies while
~10% show spiral structure; the remaining lenses have lenticular morphologies.
Spectroscopic redshifts for the lens and source are available for every system,
making SLACS the largest homogeneous dataset of galaxy-scale lenses to date. We
have developed a novel Bayesian stellar population analysis code to determine
robust stellar masses with accurate error estimates. We apply this code to
deep, high-resolution HST imaging and determine stellar masses with typical
statistical errors of 0.1 dex; we find that these stellar masses are unbiased
compared to estimates obtained using SDSS photometry, provided that informative
priors are used. The stellar masses range from 10^10.5 to 10^11.8 M and
the typical stellar mass fraction within the Einstein radius is 0.4, assuming a
Chabrier IMF. The ensemble properties of the SLACS lens galaxies, e.g. stellar
masses and projected ellipticities, appear to be indistinguishable from other
SDSS galaxies with similar stellar velocity dispersions. This further supports
that SLACS lenses are representative of the overall population of massive
early-type galaxies with M* >~ 10^11 M, and are therefore an ideal
dataset to investigate the kpc-scale distribution of luminous and dark matter
in galaxies out to z ~ 0.5.Comment: 20 pages, 18 figures, 5 tables, published in Ap
High resolution observations and mass modelling of the CLASS gravitational lens B1152+199
We present a series of high resolution radio and optical observations of the
CLASS gravitational lens system B1152+199 obtained with the Multi-Element
Radio-Linked Interferometer Network (MERLIN), Very Long Baseline Array (VLBA)
and Hubble Space Telescope (HST). Based on the milliarcsecond-scale
substructure of the lensed radio components and precise optical astrometry for
the lensing galaxy, we construct models for the system and place constraints on
the galaxy mass profile. For a single galaxy model with surface mass density
Sigma(r) propto r^-beta, we find that 0.95 < beta < 1.21 at 2-sigma confidence.
Including a second deflector to represent a possible satellite galaxy of the
primary lens leads to slightly steeper mass profiles.Comment: 7 pages, post-referee revision for MNRA
CLASS B2108+213: A new wide separation gravitational lens system
We present observations of CLASS B2108+213, the widest separation
gravitational lens system discovered by the Cosmic Lens All-Sky Survey. Radio
imaging using the VLA at 8.46 GHz and MERLIN at 5 GHz shows two compact
components separated by 4.56 arcsec with a faint third component in between
which we believe is emission from a lensing galaxy. 5-GHz VLBA observations
reveal milliarcsecond-scale structure in the two lensed images that is
consistent with gravitational lensing. Optical emission from the two lensed
images and two lensing galaxies within the Einstein radius is detected in
Hubble Space Telescope imaging. Furthermore, an optical gravitational arc,
associated with the strongest lensed component, has been detected. Surrounding
the system are a number of faint galaxies which may help explain the wide image
separation. A plausible mass distribution model for CLASS B2108+213 is also
presented.Comment: 9 pages, 8 figures, accepted for publication in MNRA
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