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 87^{87}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 $s$- and $d$- 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 $s$- and d-wave scattering amplitudes from the zero-energy limit up to the first Ramsauer minimum using only the Van der Waals $C_{6}$ coefficient as theoretical input. For the $^{87}$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 à l’affirmation de l’identité chez nombre de groupes dont les territoires se jouxtent ou partagent un même espace. Chez les groupes en contact avec d’autres langues et cultures que la leur, l’affirmation des spécificités linguistiques et culturelles en toponymie peut parfois se révéler délicate. Pour nommer les lieux, les humains disposent d’un arsenal de stratégies dénominatives, tant pour faire étalage des spécificités de leur groupe d’appartenance que pour dissimuler des particularismes susceptibles d’attirer sur eux une attention non recherchée. Dans cet article, les exemples sont tirés d’un répertoire 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 période qui précède celle de la colonisation, elle se raréfie remarquablement, toutes proportions gardées, dès les premières décennies du XXe siècle. Pour pallier les difficultés que représente ce mode de dénomination identitaire, on a eu recours, en certains endroits, à une hiéronymie dédicatoire supplétive.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 afirmación 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 afirmación de especifidades lingüísticas y culturales en toponimia puede ser difícil. Para denominar lugares, los humanos disponen de todo un arsenal de estrategias denominativas, sea para hacer ostentación de aspectos específicos del grupo de pertenencia o para disimular particularismos susceptibles de llamar una atención no deseada. En este artículo se presentan ejemplos de un repertorio de 2500 topónimos de origen y de influencia francesa en Saskachewan. Mientras que la hagionimia católica y francesa abunda en esta provincia durante el periodo que precede al de la colonización, se observa su rarefacción, teniendo en cuenta las proporciones, durante los primeros decenios del siglo XX. Para superar las dificultades de ese modo de denominación 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