164,087 research outputs found
Observation of Phase Defects in Quasi-2D Bose-Einstein Condensates
We have observed phase defects in quasi-2D Bose-Einstein condensates close to
the condensation temperature. Either a single or several equally spaced
condensates are produced by selectively evaporating the sites of a 1D optical
lattice. When several clouds are released from the lattice and allowed to
overlap, dislocation lines in the interference patterns reveal nontrivial phase
defects
Lower-dimension vacuum defects in lattice Yang-Mills theory
We overview lattice data on d=1,2,3 vacuum defects in four-dimensional
gluodynamics. In all the cases defects have total volume which scales in
physical units (with zero fractal dimension). In case of d=1,2 the defects are
distinguished by ultraviolet divergent non-Abelian action as well. This
sensitivity to the ultraviolet scale allows to derive from the continuum theory
strong constraints on the properties of the defects. The constraints turn to be
satisfied by the lattice data. In the SU(2) case we introduce a classification
scheme of the defects which allows to (at least) visualize the defect
properties in a simple and unified way. Not-yet-checked relation of the defects
to the spontaneous chiral symmetry breaking is suggested by the scheme.Comment: 19 pages Dedicated to Yuri A. Simonov on his 70th birthda
Energetics of intrinsic point defects in ZrSiO
Using first principles calculations we have studied the formation energies,
electron and hole affinities, and electronic levels of intrinsic point defects
in zircon. The atomic structures of charged interstitials, vacancies, Frenkel
pairs and anti-site defects are obtained. The limit of high concentration of
point defects, relevant for the use of this material in nuclear waste
immobilization, was studied with a variable lattice relaxation that can
simulate the swelling induced by radiation damage. The limit of low
concentration of defects is simulated with larger cells and fixed lattice
parameters. Using known band offset values at the interface of zircon with
silicon, we analyze the foreseeable effect of the defects on the electronic
properties of zircon used as gate in metal-oxide-semiconductor devices.Comment: preprint 16 pages, 4 figures, and 5 table
Anomalous far infrared monochromatic transmission through a film of type-II superconductor in magnetic field
Anomalous far infrared monochromatic transmission through a lattice of
Abrikosov vortices in a type-II superconducting film is found and reported. The
transmitted frequency corresponds to the photonic mode localized by the defects
of the Abrokosov lattice. These defects are formed by extra vortices placed out
of the nodes of the ideal Abrokosov lattice. The extra vortices can be pinned
by crystal lattice defects of a superconductor. The corresponding frequency is
studied as a function of magnetic field and temperature in the framework of the
Dirac-type two-band model. While our approach is valid for all type-II
superconductors, the specific calculations have been performed for the
YBaCuO (YBCO). The control of the transmitted
frequency by varying magnetic field and/or temperature is analyzed. It is
suggested that found anomalously transmitted localized mode can be utilized in
the far infrared monochromatic filters.Comment: 9 pages, 2 figure
Nematic cells with defect-patterned alignment layers
Using Monte Carlo simulations of the Lebwohl--Lasher model we study the
director ordering in a nematic cell where the top and bottom surfaces are
patterned with a lattice of point topological defects of lattice
spacing . We find that the nematic order depends crucially on the ratio of
the height of the cell to . When the system is very
well--ordered and the frustration induced by the lattice of defects is relieved
by a network of half--integer defect lines which emerge from the point defects
and hug the top and bottom surfaces of the cell. When the
system is disordered and the half--integer defect lines thread through the cell
joining point defects on the top and bottom surfaces. We present a simple
physical argument in terms of the length of the defect lines to explain these
results. To facilitate eventual comparison with experimental systems we also
simulate optical textures and study the switching behavior in the presence of
an electric field
Radial solitons in armchair carbon nanotubes
Radial solitons are investigated in armchair carbon nanotubes using a
generalized Lennard-Jones potential. The radial solitons are found in terms of
moving kink defects whose velocity obeys a dispersion relation. Effects of
lattice discreteness on the shape of kink defects are examined by estimating
the Peierls stress. Results suggest that the typical size for an unpinned kink
phase is of the order of a lattice spacing.Comment: 11 pages, 3(eps) figure
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