2,219 research outputs found
Fractional Chern insulators of few bosons in a box: Hall plateaus from center-of-mass drifts and density profiles
Realizing strongly-correlated topological phases of ultracold gases is a
central goal for ongoing experiments. And while fractional quantum Hall states
could soon be implemented in small atomic ensembles, detecting their signatures
in few-particle settings remains a fundamental challenge. In this work, we
numerically analyze the center-of-mass Hall drift of a small ensemble of
hardcore bosons, initially prepared in the ground state of the
Harper-Hofstadter-Hubbard model in a box potential. By monitoring the Hall
drift upon release, for a wide range of magnetic flux values, we identify an
emergent Hall plateau compatible with a fractional Chern insulator state: the
extracted Hall conductivity approaches a fractional value determined by the
many-body Chern number, while the width of the plateau agrees with the spectral
and topological properties of the prepared ground state. Besides, a direct
application of Streda's formula indicates that such Hall plateaus can also be
directly obtained from static density-profile measurements. Our calculations
suggest that fractional Chern insulators can be detected in cold-atom
experiments, using available detection methods.Comment: 13 pages, 11 figures; extended version accepted for publicatio
Interferometric determination of the s- and d-wave scattering amplitudes in Rb
We demonstrate an interference method to determine the low-energy elastic
scattering amplitudes of a quantum gas. We linearly accelerate two ultracold
atomic clouds up to energies of 1.2 mK and observe the collision halo by direct
imaging in free space. From the interference between - and - partial
waves in the differential scattering pattern we extract the corresponding phase
shifts. The method does not require knowledge of the atomic density. This
allows us to infer accurate values for the - and d-wave scattering
amplitudes from the zero-energy limit up to the first Ramsauer minimum using
only the Van der Waals coefficient as theoretical input. For the
Rb triplet potential, the method reproduces the scattering length with
an accuracy of 6%.Comment: 4 pages, 3 figure
Multiple Functionality in Nanotube Transistors
Calculations of quantum transport in a carbon nanotube transistor show that
such a device offers unique functionality. It can operate as a ballistic
field-effect transistor, with excellent characteristics even when scaled to 10
nm dimensions. At larger gate voltages, channel inversion leads to resonant
tunneling through an electrostatically defined nanoscale quantum dot. Thus the
transistor becomes a gated resonant tunelling device, with negative
differential resistance at a tunable threshold. For the dimensions considered
here, the device operates in the Coulomb blockade regime, even at room
temperature.Comment: To appear in Phys. Rev. Let
D’une hagionymie abondante à une hiéronymie supplétive. Usage d’une stratégie toponymique chez les Franco-Canadiens de la Saskatchewan
La toponymie participe Ă l’affirmation de l’identitĂ© chez nombre de groupes dont les territoires se jouxtent ou partagent un mĂŞme espace. Chez les groupes en contact avec d’autres langues et cultures que la leur, l’affirmation des spĂ©cificitĂ©s linguistiques et culturelles en toponymie peut parfois se rĂ©vĂ©ler dĂ©licate. Pour nommer les lieux, les humains disposent d’un arsenal de stratĂ©gies dĂ©nominatives, tant pour faire Ă©talage des spĂ©cificitĂ©s de leur groupe d’appartenance que pour dissimuler des particularismes susceptibles d’attirer sur eux une attention non recherchĂ©e. Dans cet article, les exemples sont tirĂ©s d’un rĂ©pertoire de près de 2500 toponymes d’origine et d’influence françaises en Saskatchewan. Alors que l’hagionymie catholique et française abonde dans cette province au cours de la pĂ©riode qui prĂ©cède celle de la colonisation, elle se rarĂ©fie remarquablement, toutes proportions gardĂ©es, dès les premières dĂ©cennies du XXe siècle. Pour pallier les difficultĂ©s que reprĂ©sente ce mode de dĂ©nomination identitaire, on a eu recours, en certains endroits, Ă une hiĂ©ronymie dĂ©dicatoire supplĂ©tive.Toponymy plays an important role in declaring identity among groups with adjoining territories as well as with those sharing the same space. Affirmation of cultural and linguistic identity through toponymy can sometimes prove to be a delicate undertaking, however. Groups in contact with languages and cultures other than their own have at their disposal an array of denominative strategies both to highlight the unique features of the group to which they belong, and to conceal aspects likely to attract unwanted attention. The examples quoted in this article are drawn from a repertoire of close to 2500 toponyms, of native and French origin, from Saskatchewan. Although Catholic and French hieronymy was prominent in Saskatchewan during the period before colonization, it had – relatively speaking – declined significantly by the turn of the twentieth century. To offset the difficulties inherent to this kind of identity-bound denomination, in certain instances a dedicatory suppletive hieronymic approach was prefered.La toponimia toma parte en la afirmaciĂłn de la identidad de numerosos grupos cuyos territorios se yuxtaponen o que comparten el mismo espacio. Para los grupos que están en contacto con otras lenguas y culturas que la suya, la afirmaciĂłn de especifidades lingĂĽĂsticas y culturales en toponimia puede ser difĂcil. Para denominar lugares, los humanos disponen de todo un arsenal de estrategias denominativas, sea para hacer ostentaciĂłn de aspectos especĂficos del grupo de pertenencia o para disimular particularismos susceptibles de llamar una atenciĂłn no deseada. En este artĂculo se presentan ejemplos de un repertorio de 2500 topĂłnimos de origen y de influencia francesa en Saskachewan. Mientras que la hagionimia catĂłlica y francesa abunda en esta provincia durante el periodo que precede al de la colonizaciĂłn, se observa su rarefacciĂłn, teniendo en cuenta las proporciones, durante los primeros decenios del siglo XX. Para superar las dificultades de ese modo de denominaciĂłn identitaria, se recurre, en ciertos lugares, a una hieronimia dedicatoria y supletoria
Negative differential resistance in nanotube devices
Carbon nanotube junctions are predicted to exhibit negative differential
resistance, with very high peak-to-valley current ratios even at room
temperature. We treat both nanotube p-n junctions and undoped
metal-nanotube-metal junctions, calculating quantum transport through the
self-consistent potential within a tight-binding approximation. The undoped
junctions in particular may be suitable for device integration.Comment: 4 pages, 4 figures, to appear in Physical Review Letter
Epitaxial growth in dislocation-free strained alloy films: Morphological and compositional instabilities
The mechanisms of stability or instability in the strained alloy film growth
are of intense current interest to both theorists and experimentalists. We
consider dislocation-free, coherent, growing alloy films which could exhibit a
morphological instability without nucleation. We investigate such strained
films by developing a nonequilibrium, continuum model and by performing a
linear stability analysis. The couplings of film-substrate misfit strain,
compositional stress, deposition rate, and growth temperature determine the
stability of film morphology as well as the surface spinodal decomposition. We
consider some realistic factors of epitaxial growth, in particular the
composition dependence of elastic moduli and the coupling between top surface
and underlying bulk of the film. The interplay of these factors leads to new
stability results. In addition to the stability diagrams both above and below
the coherent spinodal temperature, we also calculate the kinetic critical
thickness for the onset of instability as well as its scaling behavior with
respect to misfit strain and deposition rate. We apply our results to some real
growth systems and discuss the implications related to some recent experimental
observations.Comment: 26 pages, 13 eps figure
Nanoscale periodicity in stripe-forming systems at high temperature: Au/W(110)
We observe using low-energy electron microscopy the self-assembly of
monolayer-thick stripes of Au on W(110) near the transition temperature between
stripes and the non-patterned (homogeneous) phase. We demonstrate that the
amplitude of this Au stripe phase decreases with increasing temperature and
vanishes at the order-disorder transition (ODT). The wavelength varies much
more slowly with temperature and coverage than theories of stress-domain
patterns with sharp phase boundaries would predict, and maintains a finite
value of about 100 nm at the ODT. We argue that such nanometer-scale stripes
should often appear near the ODT.Comment: 5 page
Long-Range Ordering of Vibrated Polar Disks
Vibrated polar disks have been used experimentally to investigate collective
motion of driven particles, where fully-ordered asymptotic regimes could not be
reached. Here we present a model reproducing quantitatively the single, binary
and collective properties of this granular system. Using system sizes not
accessible in the laboratory, we show in silico that true long-range order is
possible in the experimental system. Exploring the model's parameter space, we
find a phase diagram qualitatively different from that of dilute or point-like
particle systems.Comment: 5 pages, 4 figure
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