851 research outputs found
Persistent currents in Bose gases confined in annular traps
We examine the problem of stability of persistent currents in a mixture of
two Bose gases trapped in an annular potential. We evaluate the critical
coupling for metastability in the transition from quasi-one to two-dimensional
motion. We also evaluate the critical coupling for metastability in a mixture
of two species as function of the population imbalance. The stability of the
currents is shown to be sensitive to the deviation from one-dimensional motion.Comment: 6 pages, 4 figure
Phase diagram of a rapidly-rotating two-component Bose gas
We derive analytically the phase diagram of a two-component Bose gas confined
in an anharmonic potential, which becomes exact and universal in the limit of
weak interactions and small anharmonicity of the trapping potential. The
transitions between the different phases, which consist of vortex states of
single and multiple quantization, are all continuous because of the addition of
the second component.Comment: 5 pages, 3 figure
Rotational properties of non-dipolar and dipolar Bose-Einstein condensates confined in annular potentials
We investigate the rotational response of both non-dipolar and dipolar
Bose-Einstein condensates confined in an annular potential. For the non-dipolar
case we identify certain critical rotational frequencies associated with the
formation of vortices. For the dipolar case, assuming that the dipoles are
aligned along some arbitrary and tunable direction, we study the same problem
as a function of the orientation angle of the dipole moment of the atoms.Comment: 5 pages, 4 figure
Optical response of two-dimensional few-electron concentric double quantum rings: A local-spin-density-functional theory study
We have investigated the dipole charge- and spin-density response of
few-electron two-dimensional concentric nanorings as a function of the
intensity of a perpendicularly applied magnetic field. We show that the dipole
response displays signatures associated with the localization of electron
states in the inner and outer ring favored by the perpendicularly applied
magnetic field. Electron localization produces a more fragmented spectrum due
to the appearance of additional edge excitations in the inner and outer ring.Comment: To be published in Physical Review
Mixtures of Bose gases confined in concentrically coupled annular traps
A two-component Bose-Einstein condensate confined in an axially-symmetric
potential with two local minima, resembling two concentric annular traps, is
investigated. The system shows a number of quantum phase transitions that
result from the competition between phase coexistence, and radial/azimuthal
phase separation. The ground-state phase diagram, as well as the rotational
properties, including the (meta)stability of currents in this system, are
analysed.Comment: 6 pages, 5 figures, minor revision
Electronic structure of few-electron concentric double quantum rings
The ground state structure of few-electron concentric double quantum rings is
investigated within the local spin density approximation. Signatures of
inter-ring coupling in the addition energy spectrum are identified and
discussed. We show that the electronic configurations in these structures can
be greatly modulated by the inter-ring distance: At short and long distances
the low-lying electron states localize in the inner and outer rings,
respectively, and the energy structure is essentially that of an isolated
single quantum ring. However, at intermediate distances the electron states
localized in the inner and the outer ring become quasi-degenerate and a rather
entangled, strongly-correlated system is formed.Comment: 16 pages (preprint format), 6 figure
Spin-orbit-coupled Bose-Einstein-condensed atoms confined in annular potentials
A spin-orbit-coupled Bose-Einstein-condensed cloud of atoms confined in an
annular trapping potential shows a variety of phases that we investigate in the
present study. Starting with the non-interacting problem, the homogeneous phase
that is present in an untrapped system is replaced by a sinusoidal density
variation in the limit of a very narrow annulus. In the case of an untrapped
system there is another phase with a striped-like density distribution, and its
counterpart is also found in the limit of a very narrow annulus. As the width
of the annulus increases, this picture persists qualitatively. Depending on the
relative strength between the inter- and the intra-components, interactions
either favor the striped phase, or suppress it, in which case either a
homogeneous, or a sinusoidal-like phase appears. Interactions also give rise to
novel solutions with a nonzero circulation.Comment: Final, slightly revised versio
Magnetic field dependence of hole levels in self-assembled InAs quantum dots
Recent magneto-transport experiments of holes in InGaAs quantum dots [D.
Reuter, P. Kailuweit, A.D. Wieck, U. Zeitler, O. Wibbelhoff, C. Meier, A.
Lorke, and J.C. Maan, Phys. Rev. Lett. 94, 026808 (2005)] are interpreted by
employing a multi-band kp Hamiltonian, which considers the interaction between
heavy hole and light hole subbands explicitely. No need of invoking an
incomplete energy shell filling is required within this model. The crucial role
we ascribe to the heavy hole-light hole interaction is further supported by
one-band local-spin-density functional calculations, which show that Coulomb
interactions do not induce any incomplete hole shell filling and therefore
cannot account for the experimental magnetic field dispersion.Comment: 5 pages with 3 figures and one table. The paper has been submitted to
Phys.Rev.
Influencia del granallado en los aceros inoxidables austenÃticos metaestables
En el presente trabajo se muestra el efecto del granallado sobre la microestructura y las propiedades mecánicas de un acero inoxidable austenÃtico metaestable EN 1.4318 (AISI 301LN). Se han considerado dos condiciones de partida distintas: recocido (microestructura totalmente austenÃtica) y laminado en frÃo (con un porcentaje inicial de martensita del 38%). La granalla utilizada es de acero inoxidable S300, proyectada a una velocidad de 65 m/s con factores de cobertura del 200 y 400%. El análisis microestructural se ha llevado a cabo por difracción de rayos-X, microscopÃa láser confocal (CLSM) y microscopÃa electrónica de barrido (MEB). Para cada condición se han realizado ensayos de fatiga a alto número de ciclos. Los resultados ponen de manifiesto que el proceso de granallado permite aumentar en un 25% el lÃmite a fatiga del acero laminado, mientras que no se observa ningún efecto sobre el acero recocido. Para esta condición, la creación de microgrietas en la superficie enmascara el efecto beneficioso del endurecimiento debido a la formación de martensita por deformación durante el proceso de granallado.The aim of this work is to study the microstructural changes and its effect on mechanical properties of a metastable austenitic stainless steel grade EN 1.4318 (AISI 301LN) subjected to shot peening process. Two different material conditions were considered: annealed (totally austenitic microstructure) and cold rolled (with an initial martensite content of 38%). Stainless steel shots type S300 impacted the surface at 65 m/s with two different coverage factors: 200 and 400%. Microstructural analysis was performed by x-ray diffraction, Confocal Laser Scanning Microscopy (CLSM) and Scanning Electron Microscopy (SEM). For each condition fatigue tests at high number of cycles were carried out. Results point out that only cold rolled samples displayed an improvement of 25% on the fatigue limit while no effect was detected for annealed steel. For this condition, the presence of surface microcracks was expected to offset the advantages introduced by the presence of deformation induced martensite formed during shot peening process.Peer Reviewe
Spin-orbit effects on the Larmor dispersion relation in GaAs quantum wells
We have studied the relevance of spin-orbit coupling to the dispersion 00009
relation of the Larmor resonance observed in inelastic light scattering and
electron-spin resonance experiments on GaAs quantum wells. We show that the
spin-orbit interaction, here described by a sum of Dresselhaus and
Bychkov-Rashba terms, couples Zeeman and spin-density excitations. We have
evaluated its contribution to the spin splitting as a function of the magnetic
field , and have found that in the small limit, the spin-orbit
interaction does not contribute to the spin splitting, whereas at high magnetic
fields it yields a independent contribution to the spin splitting given by
, with being the intensity of the
Bychkov-Rashba and Dresselhaus spin-orbit terms.Comment: To be published in Physical Review
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