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 Ca4_4Al2_2O6_6Fe2_2P2_2: Comparison with LaFePO and Ca4_4Al2_2O6_6Fe2_2As2_2

We investigate the electronic structures of iron-based superconductors having perovskite-like blocking layers, %Ca$_4$Al$_2$O$_6$Fe$_2$(As$_{1-x}$P$_x$)$_2$ from first principles. Ca$_4$Al$_2$O$_6$Fe$_2$P$_2$ and Ca$_4$Al$_2$O$_6$Fe$_2$As$_2$ from first principles. Ca$_4$Al$_2$O$_6$Fe$_2$P$_2$ is found to have two hole-like Fermi surfaces around $\Gamma$, 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 Ca$_4$Al$_2$O$_6$Fe$_2$P$_2$ is also different from that of Ca$_4$Al$_2$O$_6$Fe$_2$As$_2$, in which only one Fermi surface is formed around $\Gamma$. 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 Ca$_4$Al$_2$O$_6$Fe$_2$AsP. It is found that its electronic structure is similar to that of Ca$_4$Al$_2$O$_6$Fe$_2$P$_2$ and Ca$_4$Al$_2$O$_6$Fe$_2$As$_2$ with the average crystal structure, though Ca$_4$Al$_2$O$_6$Fe$_2$AsP contains the pnictogen height disorder. We calculate the generalized susceptibility for Ca$_4$Al$_2$O$_6$Fe$_2$(As$_{1-x}$P$_x$)$_2$ 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