2,164 research outputs found
Haldane phase in the sawtooth lattice: Edge states, entanglement spectrum and the flat band
Using density matrix renormalization group numerical calculations, we study
the phase diagram of the half filled Bose-Hubbard system in the sawtooth
lattice with strong frustration in the kinetic energy term. We focus in
particular on values of the hopping terms which produce a flat band and show
that, in the presence of contact and near neighbor repulsion, three phases
exist: Mott insulator (MI), charge density wave (CDW), and the topological
Haldane insulating (HI) phase which displays edge states and particle imbalance
between the two ends of the system. We find that, even though the entanglement
spectrum in the Haldane phase is not doubly degenerate, it is in excellent
agreement with the entanglement spectrum of the Affleck-Kennedy-Lieb-Tasaki
(AKLT) state built in the Wannier basis associated with the flat band. This
emphasizes that the absence of degeneracy in the entanglement spectrum is not
necessarily a signature of a non-topological phase, but rather that the
(hidden) protecting symmetry involves non-local states. Finally, we also show
that the HI phase is stable against small departure from flatness of the band
but is destroyed for larger ones.Comment: 10 pages, 16 figure
Berry Curvature of interacting bosons in a honeycomb lattice
We consider soft-core bosons with onsite interaction loaded in the honeycomb
lattice with different site energies for the two sublattices. Using both a
mean-field approach and quantum Monte-Carlo simulations, we show that the
topology of the honeycomb lattice results in a non-vanishing Berry curvature
for the band structure of the single-particle excitations of the system. This
Berry curvature induces an anomalous Hall effect. It is seen by studying the
time evolution of a wavepacket, namely a superfluid ground state in a harmonic
trap, subjected either to a constant force (Bloch oscillations) or to a sudden
shift of the trap center.Comment: 10 pages, 11 figure
Fermi-LAT Observations of the 2014 May-July outburst from 3C 454.3
A prominent outburst of the flat spectrum radio quasar 3C~454.3 was observed
in 2014 June with the \emph{Fermi} Large Area Telescope. This outburst was
characterized by a three-stage light-curve pattern---plateau, flare and
post-flare---that occurred from 2014 May to July, in a similar pattern as
observed during the exceptional outburst in 2010 November. The highest flux of
the outburst reported in this paper occurred during 2014 June 7--29, showing a
multiple-peak structure in the light-curves. The average flux in these 22 days
was found to be ~ph~cm~s, with a spectral index, for a simple power law,
of . That made this outburst the first -ray
high state of 3C~454.3 ever to be detected by \emph{Fermi} with such a hard
spectrum over several days. The highest flux was recorded on 2014 June 15, in a
3 hr bin, at MJD 56823.5625, at a level of ~ph~cm~s. The rise time of one of the short
subflares was found to be ~s at MJD = 56827, when the flux
increased from 4 to 12 ~ph~cm~s. Several photons
above 20 GeV were collected during this outburst, including one at 45 GeV on
MJD 56827, constraining the -ray emission region to be located close to
the outer boundary of the broad-line region, leading to fast flux variability.Comment: Accepted for publication in {\sc the astrophysical journal}: 2016
July 12}; 15 pages, 7 figures, 6 table
Datation par le carbone 14 d'un niveau sédimentaire de l'archipel du lac Tchad
International audienceUne datation de 460 ans BP d'un niveau d'argile d'une carotte prélevée dans l'archipel du lac Tchad permet de situer une phase d'assèchement dans l'histoire récente du lac et de calculer une vitesse de sédimentation. Le rôle et l'importance des conditions locales sont soulignés
Submillimetre point sources from the Archeops experiment: Very Cold Clumps in the Galactic Plane
Archeops is a balloon-borne experiment, mainly designed to measure the Cosmic
Microwave Background (CMB) temperature anisotropies at high angular resolution
(~ 12 arcminutes). By-products of the mission are shallow sensitivity maps over
a large fraction of the sky (about 30 %) in the millimetre and submillimetre
range at 143, 217, 353 and 545 GHz. From these maps, we produce a catalog of
bright submillimetre point sources. We present in this paper the processing and
analysis of the Archeops point sources. Redundancy across detectors is the key
factor allowing to sort out glitches from genuine point sources in the 20
independent maps. We look at the properties of the most reliable point sources,
totalling 304. Fluxes range from 1 to 10,000 Jy (at the frequencies covering
143 to 545 GHz). All sources are either planets (2) or of galactic origin.
Longitude range is from 75 to 198 degrees. Some of the sources are associated
with well-known Lynds Nebulae and HII compact regions in the galactic plane. A
large fraction of the sources have an IRAS counterpart. Except for Jupiter,
Saturn, the Crab and Cas A, all sources show a dust-emission-like modified
blackbody emission spectrum. Temperatures cover a range from 7 to 27 K. For the
coldest sources (T<10 K), a steep nu^beta emissivity law is found with a
surprising beta ~ 3 to 4. An inverse relationship between T and beta is
observed. The number density of sources at 353 GHz with flux brighter than 100
Jy is of the order of 1 per degree of Galactic longitude. These sources will
provide a strong check for the calibration of the Planck HFI focal plane
geometry as a complement to planets. These very cold sources observed by
Archeops should be prime targets for mapping observations by the Akari and
Herschel space missions and ground--based observatories.Comment: Version matching the published article (English improved). Published
in Astron. Astrophys, 21 pages, 13 figures, 4 tables Full article (with
complete tables) can be retrieved at
http://www.archeops.org/Archeops_Publicatio
Multi-Detector Multi-Component spectral matching and applications for CMB data analysis
We present a new method for analyzing multi--detector maps containing
contributions from several components. Our method, based on matching the data
to a model in the spectral domain, permits to estimate jointly the spatial
power spectra of the components and of the noise, as well as the mixing
coefficients. It is of particular relevance for the analysis of
millimeter--wave maps containing a contribution from CMB anisotropies.Comment: 15 pages, 7 Postscript figures, submitted to MNRA
Pairing and superconductivity in the flat band: Creutz lattice
We use unbiased numerical methods to study the onset of pair superfluidity in
a system that displays flat bands in the noninteracting regime. This is
achieved by using a known example of flat band systems, namely the Creutz
lattice, where we investigate the role of local attractive interactions in the
Hubbard model. Going beyond the standard approach used in these systems
where weak interactions are considered, we map the superfluid behavior for a
wide range of interaction strengths and exhibit a crossover between BCS and
tightly bound bosonic fermion pairs. We further contrast these results with a
standard two-leg fermionic ladder, showing that the pair correlations, although
displaying algebraic decay in both cases, are longer ranged in the Creutz
lattice, signifying the robustness of pairing in this system.Comment: 11 pages, 12 figures; as publishe
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