17,678 research outputs found
Disorder Induced Stripes in d-Wave Superconductors
Stripe phases are observed experimentally in several copper-based high-Tc
superconductors near 1/8 hole doping. However, the specific characteristics may
vary depending on the degree of dopant disorder and the presence or absence of
a low- temperature tetragonal phase. On the basis of a Hartree-Fock decoupling
scheme for the t-J model we discuss the diverse behavior of stripe phases. In
particular the effect of inhomogeneities is investigated in two distinctly
different parameter regimes which are characterized by the strength of the
interaction. We observe that small concen- trations of impurities or vortices
pin the unidirectional density waves, and dopant disorder is capable to
stabilize a stripe phase in parameter regimes where homogeneous phases are
typically favored in clean systems. The momentum-space results exhibit
universal features for all coexisting density-wave solutions, nearly unchanged
even in strongly disordered systems. These coexisting solutions feature
generically a full energy gap and a particle-hole asymmetry in the density of
states.Comment: 28 pages, 8 figure
Device for in-situ cleaving of hard crystals
Cleaving crystals in a vacuum chamber is a simple method for obtaining
atomically flat and clean surfaces for materials that have a preferential
cleaving plane. Most in-situ cleavers use parallel cutting edges that are
applied from two sides on the sample. We found in ambient experiments that
diagonal cutting pliers, where the cleavage force is introduced in a single
point instead of a line work very well also for hard materials. Here, we
incorporate the diagonal cutting plier principle in a design compatible with
ultra-high vacuum requirements. We show optical microscopy (mm scale) and
atomic force microscopy (atomic scale) images of NiO(001) surfaces cleaved with
this device.Comment: 7 pages, 3 figures Submitted to Review of Scientific Instruments
(2005
Raman Scattered He II 6545 Line in the Symbiotic Star V1016 Cygni
We present a spectrum of the symbiotic star V1016 Cyg observed with the 3.6 m
Canada-France-Hawaii Telescope, in order to illustrate a method to measure the
covering factor of the neutral scattering region around the giant component
with respect to the hot emission region around the white dwarf component. In
the spectrum, we find broad wings around H and a broad emission feature
around 6545 that is blended with the [N II] 6548 line.
These two features are proposed to be formed by Raman scattering by atomic
hydrogen, where the incident radiation is proposed to be UV continuum radiation
around Ly in the former case and He II 1025 emission line
arising from transitions for the latter feature. We remove the
H wings by a template Raman scattering wing profile and subtract the [N
II] 6548 line using the 3 times stronger [N II] 6583
feature in order to isolate the He II Raman scattered 6545 \AA line. We obtain
the flux ratio of the He II 6560 emission
line and the 6545 \AA feature for V1016 Cyg. Under the assumption that the He
II emission from this object is isotropic, this ratio is converted to the ratio
of the number of the incident photons and that
of the scattered photons. This implies that the scattering region with H I
column density covers 17 per cent of the
emission region. By combining the presumed binary period yrs of this
system we infer that a significant fraction of the slow stellar wind from the
Mira component is ionized and that the scattering region around the Mira
extends a few tens of AU, which is closely associated with the mass loss
process of the Mira component.Comment: 12 pages, 6 figures, accepted for publication in Ap
Understanding the dynamical structure of pulsating stars. HARPS spectroscopy of the delta Scuti stars rho Pup and DX Cet
High-resolution spectroscopy is a powerful tool to study the dynamical
structure of pulsating stars atmosphere. We aim at comparing the line asymmetry
and velocity of the two delta Sct stars rho Pup and DX Cet with previous
spectroscopic data obtained on classical Cepheids and beta Cep stars. We
obtained, analysed and discuss HARPS high-resolution spectra of rho Pup and DX
Cet. We derived the same physical quantities as used in previous studies, which
are the first-moment radial velocities and the bi-Gaussian spectral line
asymmetries. The identification of f=7.098 (1/d) as a fundamental radial mode
and the very accurate Hipparcos parallax promote rho Pup as the best standard
candle to test the period-luminosity relations of delta Sct stars. The action
of small-amplitude nonradial modes can be seen as well-defined cycle-to-cycle
variations in the radial velocity measurements of rho Pup. Using the
spectral-line asymmetry method, we also found the centre-of-mass velocities of
rho Pup and DX Cet, V_gamma = 47.49 +/- 0.07 km/s and V_gamma = 25.75 +/- 0.06
km/s, respectively. By comparing our results with previous HARPS observations
of classical Cepheids and beta Cep stars, we confirm the linear relation
between the atmospheric velocity gradient and the amplitude of the radial
velocity curve, but only for amplitudes larger than 22.5 km/s. For lower values
of the velocity amplitude (i.e., < 22.5 km/s), our data on rho Pup seem to
indicate that the velocity gradient is null, but this result needs to be
confirmed with additional data. We derived the Baade-Wesselink projection
factor p = 1.36 +/- 0.02 for rho Pup and p = 1.39 +/- 0.02 for DX Cet. We
successfully extended the period-projection factor relation from classical
Cepheids to delta Scuti stars.Comment: Accepted for publication in A&A (in press
Probing of the Kondo peak by the impurity charge measurement
We consider the real-time dynamics of the Kondo system after the local probe
of the charge state of the magnetic impurity. Using the exactly solvable
infinite-degeneracy Anderson model we find explicitly the evolution of the
impurity charge after the measurement.Comment: 4 pages, 1 eps figure, revte
Variational Calculations of the Nucleus Structure in a 3 Model Using a Deep Potential with Forbidden States
The energy spectrum of the nucleus with and
is investigated in the framework of the multicluster dynamical model
by using a deep -potential with forbidden states in the S and D
waves. A very high sensitivity of the compact ground and first excited
states energy levels to the description of the two-body forbidden states wave
functions has been estabilished. It is shown also that the chosen method of
orthogonalizing pseudopotentials yields convergent results for the energies of
the excited and states of the nucleus with a
well developed cluster like structure
Non-linear optomechanical measurement of mechanical motion
Precision measurement of non-linear observables is an important goal in all
facets of quantum optics. This allows measurement-based non-classical state
preparation, which has been applied to great success in various physical
systems, and provides a route for quantum information processing with otherwise
linear interactions. In cavity optomechanics much progress has been made using
linear interactions and measurement, but observation of non-linear mechanical
degrees-of-freedom remains outstanding. Here we report the observation of
displacement-squared thermal motion of a micro-mechanical resonator by
exploiting the intrinsic non-linearity of the radiation pressure interaction.
Using this measurement we generate bimodal mechanical states of motion with
separations and feature sizes well below 100~pm. Future improvements to this
approach will allow the preparation of quantum superposition states, which can
be used to experimentally explore collapse models of the wavefunction and the
potential for mechanical-resonator-based quantum information and metrology
applications.Comment: 8 pages, 4 figures, extensive supplementary material available with
published versio
Mutations in human dynamin block an intermediate stage in coated vesicle formation
The role of human dynamin in receptor-mediated endocytosis was investigated by transient expression of GTP-binding domain mutants in mammalian cells. Using assays which detect intermediates in coated vesicle formation, the dynamin mutants were found to block endocytosis at a stage after the initiation of coat assembly and preceding the sequestration of ligands into deeply invaginated coated pits. Membrane transport from the ER to the Golgi complex was unaffected indicating that dynamin mutants specifically block early events in endocytosis. These results demonstrate that mutations in the GTP-binding domain of dynamin block Tfn-endocytosis in mammalian cells and suggest that a functional dynamin GTPase is required for receptor-mediated endocytosis via clathrin-coated pits
Continuum coupled cluster expansion
We review the basics of the coupled-cluster expansion formalism for numerical
solutions of the many-body problem, and we outline the principles of an
approach directed towards an adequate inclusion of continuum effects in the
associated single-energy spectrum. We illustrate our findings by considering
the simple case of a single-particle quantum mechanics problem.Comment: 16 pages, 1 figur
Maser Oscillation in a Whispering-Gallery-Mode Microwave Resonator
We report the first observation of above-threshold maser oscillation in a
whispering-gallery(WG)-mode resonator, whose quasi-transverse-magnetic, 17th
azimuthal-order WG mode, at a frequency of approx. 12.038 GHz, with a loaded Q
of several hundred million, is supported on a cylinder of mono-crystalline
sapphire. An electron spin resonance (ESR) associated with Fe3+ ions, that are
substitutively included within the sapphire at a concentration of a few parts
per billion, coincides in frequency with that of the (considerably narrower) WG
mode. By applying a c.w. `pump' to the resonator at a frequency of approx.
31.34 GHz, with no applied d.c. magnetic field, the WG (`signal') mode is
energized through a three-level maser scheme. Preliminary measurements
demonstrate a frequency stability (Allan deviation) of a few times 1e-14 for
sampling intervals up to 100 s.Comment: REVTeX v.4, 3 pages, with a separate .bbl file and 3 .eps figure
- âŠ