127,771 research outputs found
Coherent Graphene Devices: Movable Mirrors, Buffers and Memories
We theoretically report that, at a sharp electrostatic step potential in
graphene, massless Dirac fermions can obtain Goos-H\"{a}nchen-like shifts under
total internal reflection. Based on these results, we study the coherent
propagation of the quasiparticles along a sharp graphene \emph{p-n-p} waveguide
and derive novel dispersion relations for the guided modes. Consequently,
coherent graphene devices (e.g. movable mirrors, buffers and memories) induced
only by the electric field effect can be proposed.Comment: 12 pages, 5 figure
Diffusion induced decoherence of stored optical vortices
We study the coherence properties of optical vortices stored in atomic
ensembles. In the presence of thermal diffusion, the topological nature of
stored optical vortices is found not to guarantee slow decoherence. Instead the
stored vortex state has decoherence surprisingly larger than the stored
Gaussian mode. Generally, the less phase gradient, the more robust for stored
coherence against diffusion. Furthermore, calculation of coherence factor shows
that the center of stored vortex becomes completely incoherent once diffusion
begins and, when reading laser is applied, the optical intensity at the center
of the vortex becomes nonzero. Its implication for quantum information is
discussed. Comparison of classical diffusion and quantum diffusion is also
presented.Comment: 5 pages, 2 figure
Calibrating the {\alpha} parameter of convective efficiency using observed stellar properties
Context. Synthetic model atmosphere calculations are still the most commonly
used tool when determining precise stellar parameters and stellar chemical
compositions. Besides three-dimensional models that consistently solve for
hydrodynamic processes, one-dimensional models that use an approximation for
convective energy transport play the major role.
Aims. We use modern Balmer-line formation theory as well as spectral energy
distribution (SED) measurements for the Sun and Procyon to calibrate the model
parameter {\alpha} that describes the efficiency of convection in our 1D
models. Convection was calibrated over a significant range in parameter space,
reaching from F-K along the main sequence and sampling the turnoff and giant
branch over a wide range of metallicities. This calibration was compared to
theoretical evaluations and allowed an accurate modeling of stellar
atmospheres.
Methods. We used Balmer-line fitting and SED fits to determine the convective
efficiency parameter {\alpha}. Both methods are sensitive to the structure and
temperature stratification of the deeper photosphere.
Results. While SED fits do not allow a precise determination of the
convective parameter for the Sun and Procyon, they both favor values
significantly higher than 1.0. Balmer-line fitting, which we find to be more
sensitive, suggests that the convective efficiency parameter {\alpha} is
2.0 for the main sequence and quickly decreases to 1.0 for
evolved stars. These results are highly consistent with predictions from 3D
models. While the values on the main sequence fit predictions very well,
measurements suggest that the decrease of convective efficiency as stars evolve
to the giant branch is more dramatic than predicted by models.Comment: 14 pages, 16 figures, accepted for publication in A&
Anomalous Hall effect in L10-MnAl films with controllable orbital two-channel Kondo effect
The anomalous Hall effect (AHE) in strongly disordered magnetic systems has
been buried in persistent confusion despite its long history. We report the AHE
in perpendicularly magnetized L10-MnAl epitaxial films with variable orbital
two-channel Kondo (2CK) effect arising from the strong coupling of conduction
electrons and the structural disorders of two-level systems. The AHE is
observed to excellently scale with pAH/f=a0pxx0+bpxx2 at high temperatures
where phonon scattering prevails. In contrast, significant deviation occurs at
low temperatures where the orbital 2CK effect becomes important, suggesting a
negative AHE contribution. The deviation of the scaling agrees with the orbital
2CK effect in the breakdown temperatures and deviation magnitudes
Averages of shifted convolutions of
We investigate the first and second moments of shifted convolutions of the
generalised divisor function .Comment: 22 page
Characterization of the residual stresses in spray-formed steels using neutron diffraction
Neutron diffraction was used to characterize the residual stresses in an as-sprayed tube-shaped steel preform. The measured residual stress distributions were compared with those simulated using finite element method by taking into account the effects of the thermal history, porosity and different phases of the sprayed preform. The porosity was measured using X-ray microcomputed tomography. The study revealed for the first time the correlation between the distribution of porosity and residual stress developed in the as-sprayed preform
Dephasing time in graphene due to interaction with flexural phonons
We investigate decoherence of an electron in graphene caused by
electron-flexural phonon interaction. We find out that flexural phonons can
produce dephasing rate comparable to the electron-electron one. The problem
appears to be quite special because there is a large interval of temperature
where the dephasing induced by phonons can not be obtain using the golden rule.
We evaluate this rate for a wide range of density () and temperature ()
and determine several asymptotic regions with temperature dependence crossing
over from to when
temperature increases. We also find to be a non-monotonous
function of . These distinctive features of the new contribution can provide
an effective way to identify flexural phonons in graphene through the
electronic transport by measuring the weak localization corrections in
magnetoresistance.Comment: 13 pages, 8 figure
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