1,367 research outputs found
Composite Fermion Pairing in Bilayer Quantum Hall Systems
We derive the effective Hamiltonian for the composite fermion in double-layer
quantum Hall systems with inter-layer tunneling at total Landau-level filling
factor , where is an integer. We find that the ground state is the
triplet p-wave BCS pairing state of the composite fermions. At , the
ground state of the system evolves from the Halperin -state toward the
Pfaffian-state with increasing the tunneling amplitude. On the other hand, at
, the pairing state is uniquely determined independent of tunneling
amplitude.Comment: 13 pages, 2 figure
Doping Dependence of Anisotropic Resistivities in Trilayered Superconductor Bi2Sr2Ca2Cu3O10+delta (Bi-2223)
The doping dependence of the themopower, in-plane resistivity rho_ab(T),
out-of-plane resistivity rho_c(T), and susceptibility has been systematically
measured for high-quality single crystal Bi2Sr2Ca2Cu3O10+delta. We found that
the transition temperature Tc and pseudogap formation temperature T_rho_c*,
below which rho_c shows a typical upturn, do not change from their optimum
values in the "overdoped" region, even though doping actually proceeds. This
suggests that, in overdoped region, the bulk is determined by the always
underdoped inner plane, which have a large superconducting gap, while the
carriers are mostly doped in the outer planes, which have a large phase
stiffness.Comment: 5 pages, 4 figures. to be published in PR
Locating the most energetic electrons in Cassiopeia A
We present deep (2.4 Ms) observations of the Cassiopeia A supernova
remnant with {\it NuSTAR}, which operates in the 3--79 keV bandpass and is the
first instrument capable of spatially resolving the remnant above 15 keV. We
find that the emission is not entirely dominated by the forward shock nor by a
smooth "bright ring" at the reverse shock. Instead we find that the 15 keV
emission is dominated by knots near the center of the remnant and dimmer
filaments near the remnant's outer rim. These regions are fit with unbroken
power-laws in the 15--50 keV bandpass, though the central knots have a steeper
() spectrum than the outer filaments ().
We argue this difference implies that the central knots are located in the 3-D
interior of the remnant rather than at the outer rim of the remnant and seen in
the center due to projection effects. The morphology of 15 keV emission does
not follow that of the radio emission nor that of the low energy (12 keV)
X-rays, leaving the origin of the 15 keV emission as an open mystery. Even
at the forward shock front we find less steepening of the spectrum than
expected from an exponentially cut off electron distribution with a single
cutoff energy. Finally, we find that the GeV emission is not associated with
the bright features in the {\it NuSTAR} band while the TeV emission may be,
suggesting that both hadronic and leptonic emission mechanisms may be at work.Comment: 12 pages, 11 figures, accepted for publication in Ap
Thermodynamic properties of spontaneous magnetization in Chern-Simons QED_3
The spontaneous magnetization in Chern-Simons QED_3 is discussed in a finite
temperature system. The thermodynamical potential is analyzed within the weak
field approximation and in the fermion massless limit. We find that there is a
linear term with respect to the magnetic field with a negative coefficient at
any finite temperature. This implies that the spontaneous magnetic field does
not vanish even at high temperature. In addition, we examine the photon
spectrum in the system. We find that the bare Chern-Simons coefficient is
cancelled by the radiative effects. The photons then become topologically
massless according to the magnetization, though they are massive by finite
temperature effects. Thus the magnetic field is a long-range force without the
screening even at high temperature.Comment: 32 pages, Latex, 4 eps figure
Steady state properties of a driven granular medium
We study a two-dimensional granular system where external driving force is
applied to each particle in the system in such a way that the system is driven
into a steady state by balancing the energy input and the dissipation due to
inelastic collision between particles. The velocities of the particles in the
steady state satisfy the Maxwellian distribution. We measure the
density-density correlation and the velocity-velocity correlation functions in
the steady state and find that they are of power-law scaling forms. The
locations of collision events are observed to be time-correlated and such a
correlation is described by another power-law form. We also find that the
dissipated energy obeys a power-law distribution. These results indicate that
the system evolves into a critical state where there are neither characteristic
spatial nor temporal scales in the correlation functions. A test particle
exhibits an anomalous diffusion which is apparently similar to the Richardson
law in a three-dimensional turbulent flow.Comment: REVTEX, submitted to Phys. Rev.
Velocity and density profiles of granular flow in channels using lattice gas automaton
We have performed two-dimensional lattice-gas-automaton simulations of
granular flow between two parallel planes. We find that the velocity profiles
have non-parabolic distributions while simultaneously the density profiles are
non-uniform. Under non-slip boundary conditions, deviation of velocity profiles
from the parabolic form of newtonian fluids is found to be characterized solely
by ratio of maximal velocity at the center to the average velocity, though the
ratio depends on the model parameters in a complex manner. We also find that
the maximal velocity () at the center is a linear function of the
driving force (g) as with non-zero in
contrast with newtonian fluids. Regarding density profiles, we observe that
densities near the boundaries are higher than those in the center. The width of
higher densities (above the average density) relative to the channel width is a
decreasing function of a variable which scales with the driving force (g),
energy dissipation parameter () and the width of the system (L) as
with exponents and . A phenomenological theory based on a scaling argument is presented to
interpret these findings.Comment: Latex, 15 figures, to appear in PR
Vicinal Surface with Langmuir Adsorption: A Decorated Restricted Solid-on-solid Model
We study the vicinal surface of the restricted solid-on-solid model coupled
with the Langmuir adsorbates which we regard as two-dimensional lattice gas
without lateral interaction. The effect of the vapor pressure of the adsorbates
in the environmental phase is taken into consideration through the chemical
potential. We calculate the surface free energy , the adsorption coverage
, the step tension , and the step stiffness by
the transfer matrix method combined with the density-matrix algorithm. Detailed
step-density-dependence of and is obtained. We draw the roughening
transition curve in the plane of the temperature and the chemical potential of
adsorbates. We find the multi-reentrant roughening transition accompanying the
inverse roughening phenomena. We also find quasi-reentrant behavior in the step
tension.Comment: 7 pages, 12 figures (png format), RevTeX 3.1, submitted to Phys. Rev.
Strong Interactions of Single Atoms and Photons near a Dielectric Boundary
Modern research in optical physics has achieved quantum control of strong
interactions between a single atom and one photon within the setting of cavity
quantum electrodynamics (cQED). However, to move beyond current
proof-of-principle experiments involving one or two conventional optical
cavities to more complex scalable systems that employ N >> 1 microscopic
resonators requires the localization of individual atoms on distance scales <
100 nm from a resonator's surface. In this regime an atom can be strongly
coupled to a single intracavity photon while at the same time experiencing
significant radiative interactions with the dielectric boundaries of the
resonator. Here, we report an initial step into this new regime of cQED by way
of real-time detection and high-bandwidth feedback to select and monitor single
Cesium atoms localized ~100 nm from the surface of a micro-toroidal optical
resonator. We employ strong radiative interactions of atom and cavity field to
probe atomic motion through the evanescent field of the resonator. Direct
temporal and spectral measurements reveal both the significant role of
Casimir-Polder attraction and the manifestly quantum nature of the atom-cavity
dynamics. Our work sets the stage for trapping atoms near micro- and
nano-scopic optical resonators for applications in quantum information science,
including the creation of scalable quantum networks composed of many
atom-cavity systems that coherently interact via coherent exchanges of single
photons.Comment: 8 pages, 5 figures, Supplemental Information included as ancillary
fil
Type I ULIRGs: Transition Stage from ULIRGs to QSOs
We examine whether the ultraluminous infrared galaxies that contain a type I
Seyfert nucleus (a type I ULIRG) are in the transition stage from ULIRGs to
quasi-stellar objects (QSOs). To inspect this issue, we compare the black hole
(BH) mass, the bulge luminosity and the far infrared luminosity among type I
ULIRGs, QSOs and elliptical galaxies. As a result, we find the following
results; (1) The type I ULIRGs have systematically smaller BH masses in spite
of the comparable bulge luminosity relative to QSOs and elliptical galaxies.
(2) The far-infrared luminosity of most type I ULIRGs is larger than the
Eddington luminosity. We show that above results do not change significantly
for 3 type I ULIRGs that we can estimate the visual extinction from the column
density. Also, for all 8 type I ULIRGs, we investigate the effect of
uncertainties of BH mass measurments and our sample bias, so that it turns out
that our results do not alter even if we consider above two effects. In
addition, Anabuki (2004) revealed that their X-ray properties are similar to
those of the narrow line Seyfert 1 galaxies. These would indicate that active
galactic nuclei (AGNs) with a high mass accretion rate exist in the type I
ULIRGs. Based on all of these findings, we conclude that it would be a natural
interpretation that type I ULIRGs are the early phase of BH growth, namely the
missing link between ULIRGs and QSOs. Moreover, by comparing our results with a
theoretical model of a coevolution scenario of a QSO BH and a galactic bulge,
we show clearly that this explanation would be valid.Comment: 11 pages, 4 figures, 4 tables accepted for publication in Ap
- …