9 research outputs found
Magnetic Properties of Ab initio Model for Iron-Based Superconductors LaFeAsO
By using variational Monte Carlo method, we examine an effective low-energy
model for LaFeAsO derived from an ab initio downfolding scheme. We show that
quantum and many-body fluctuations near a quantum critical point largely reduce
the antiferromagnetic (AF) ordered moment and the model not only quantitatively
reproduces the small ordered moment in LaFeAsO, but also explains the diverse
dependence on LaFePO, BaFe2As2 and FeTe. We also find that LaFeAsO is under
large orbital fluctuations, sandwiched by the AF Mott insulator and weakly
correlated metals. The orbital fluctuations and Dirac-cone dispersion hold keys
for the diverse magnetic properties.Comment: 4 pages, 4 figure
First-principles Electronic Structure of Superconductor CaAlOFeP: Comparison with LaFePO and CaAlOFeAs
We investigate the electronic structures of iron-based superconductors having
perovskite-like blocking layers, %CaAlOFe(AsP)
from first principles. CaAlOFeP and
CaAlOFeAs from first principles.
CaAlOFeP is found to have two hole-like Fermi surfaces
around , and one hole-like Fermi surface around M in the unfolded
Brillouin zone. This is in contrast with LaFePO, where no Fermi surface is
found around M. The relationship of their band structures and measured
transition temperatures of superconductivity is discussed. The number of Fermi
surfaces in CaAlOFeP is also different from that of
CaAlOFeAs, in which only one Fermi surface is formed around
. Analysis using maximally localized Wannier functions clarifies that
the differences between their band structures originate mainly from the
pnictogen height. We then analyze the alloying effect on the electronic
structure of CaAlOFeAsP. It is found that its electronic
structure is similar to that of CaAlOFeP and
CaAlOFeAs with the average crystal structure, though
CaAlOFeAsP contains the pnictogen height disorder. We calculate
the generalized susceptibility for CaAlOFe(AsP)
and clarify the factors determining its tendency.Comment: 5 figures, to be published in J. Phys. Soc. Jp
Study of deconfinement in NA50
The J/Ψ production in 158 A Ge V Pb-Pb interactions is studied, in the dimuon decay channel, as a function of centrality, as measured with the electromagnetic or, alternatively, with the very forward hadronic calorimeters. After a first sharp variation at mid-centrality, both patterns continue to fall down and exhibit a curvature change at high centrality values. This trend excludes any conventional hadronic model and finds a natural explanation in a deconfined quark-gluon phase scenario
Search for satellites near (21) Lutetia using OSIRIS/Rosetta images
On 2010 July 10 the ESA Rosetta mission flew by the large asteroid (21) Lutetia. One of the scientific goals of the onboard OSIRIS instrument was the search for satellites of the asteroid, with more than 20 images specifically dedicated to this topic. An observational campaign was devised with a selection of filters and exposure times tailored to maximize the possibility of detecting small companions and determining their bound orbits. Data were analyzed with suitable methods to remove cosmic ray hits and known background objects, in order to search for persistent detections of potential interesting flux sources. We found no unambiguous detections of a satellite larger than View the MathML source inside the entire sphere of gravitational influence. Our search confirmed the absence of bound companions larger than View the MathML source inside 20 primary radii. These limits are a factor of ∼30 smaller than the values reported so far from large ground-based telescopes using adaptive optics and from the Hubble Space Telescope
Hydrocode simulations of the largest crater on asteroid Lutetia
The flyby of the Main Belt asteroid Lutetia by the Rosetta spacecraft allows the camera OSIRIS to obtain very good images of about half of the body at the maximum resolution of 60 m per pixel. From the images and radio-science experiment, a density of about (3.4±0.3) g/cm3 has been inferred for the asteroid.Many impact craters have been observed on the surface of Lutetia and the largest, named Massilia, has a diameter of about 55 km. Relative to the size of Lutetia (the longest axis is approximately 126 km) the crater represents one of the dominating features on its surface. Whether or not the impact that formed Massilia affected the entire asteroid can be only evaluated via numerical modeling, with hydrocodes, of the impact process. The results of a suite of iSALE simulations are compared with the crater profile derived from the Digital Terrain Model of the observed surface. The best match to the DTM of the crater with hydrocode simulations has allowed to determine a value of 7.5 km for the impactor diameter, which suggests a primordial origin of Lutetia due to the low probability of such an impact event.A second interesting impact structure has been identified nearby Massilia within the North Pole Crater Cluster. The crater has a diameter of 24 km and it lies over a larger crater of the North Pole Crater Cluster. This is strongly suggestive of a very young structure on Lutetia. The numerical simulations of this feature constrain the impactor to be 3.8 km in diameter, assuming the same material properties for target and impactor as in the model of the formation of Massilia
Calibrations of CR39 and Makrofol nuclear track detectors and search for exotic particles
We present the final results of the search for exotic massive particles in the cosmic radiation performed with the MACRO underground experiment. Magnetic monopoles and nuclearites flux upper limits obtained with the CR39 nuclear track subdetector, the scintillation and streamer tube subdetectors are given. Searches at high altitude with the SLIM experiment are in progress