Andreev Reflection and Proximity effect

The Andreev Reflection is the key mechanism for the superconducting proximity effect. It provides phase correlations in a system of non-interacting electrons at mesoscopic scales, i.e. over distances much larger than the microscopic lengths : Fermi wavelength and elastic electron mean free path. This field of research has attracted an increasing interest in the recent years in part because of the tremendous development of nanofabrication technologies, and also because of the richness of the involved quantum effects. In this paper we review some recently achieved advances. We also discuss new open questions, in particular non-equilibrium effects and proximity effect in systems with ferromagnetic elements.Comment: 17 pages, no figure, to appear in J. of Low Temp. Phys., proceeding of the LT satellite conference "Electron Transport in Mesoscopic Systems", reference list correcte

A very low temperature STM for the local spectroscopy of mesoscopic structures

We present the design and operation of a very-low temperature Scanning Tunneling Microscope (STM) working at $60 mK$ in a dilution refrigerator. The STM features both atomic resolution and micron-sized scanning range at low temperature. This work is the first experimental realization of a local spectroscopy of mesoscopic structures at very low temperature. We present high-resolution current-voltage characteristics of tunnel contacts and the deduced local density of states of hybrid Superconductor-Normal metal systems.Comment: 5 pages, 5 figures, slightly corrected versio

Derivation of Distances with the Tully-Fisher Relation: The Antlia Cluster

The Tully-Fisher relation is a correlation between the luminosity and the HI 21cm line width in spiral galaxies (LLW relation). It is used to derive galaxy distances in the interval 7 to 100 Mpc. Closer, the Cepheids, TRGB and Surface Brightness Fluctuation methods give a better accuracy. Further, the SNIa are luminous objects still available for distance measurement purposes, though with a dramatically lower density grid of measurements on the sky. Galaxies in clusters are all at the same distance from the observer. Thus the distance of the cluster derived from a large number of galaxies (N) has an error reduced according to the square root of N. However, not all galaxies in a cluster are suitable for the LLW measurement. The selection criteria we use are explained hereafter; the important point being to avoid Malmquist bias and to not introduce any systematics in the distance measurement.Comment: Moriond0

Long-ranged magnetic proximity effects in noble metal-doped cobalt probed with spin-dependent tunnelling

We inserted non-magnetic layers of Au and Cu into sputtered AlO$_{x}$-based magnetic tunnel junctions and Meservey–Tedrow junctions in order to study their effect on tunnelling magnetoresistance (TMR) and spin polarization (TSP). When either Au or Cu are inserted into a Co/AlO$_{x}$ interface, we find that TMR and TSP remain finite and measurable for thicknesses up to several nanometres. High-resolution transmission electron microscopy shows that the Cu and Au interface layers are fully continuous when their thickness exceeds ~3nm, implying that spin-polarized carriers penetrate the interface noble metal to distances exceeding this value. A power law model based on exchange scattering is found to fit the data better than a phenomenological exponential decay. The discrepancy between these length scales and the much shorter ones reported from x-ray magnetic circular dichroism studies of magnetic proximitization is ascribed to the fact that our tunnelling transport measurements selectively probe s-like electrons close to the Fermi level. When a 0.1 nm thick Cu or Au layer is inserted within the Co, we find that the suppression of TMR and TSP is restored on a length scale of ≤ 1nm, indicating that this is a sufficient quantity of Co to form a fully spin-polarized band structure at the interface with the tunnel barrier

Noise Correlations in Three-Terminal Diffusive Superconductor-Normal Metal-Superconductor Nanostructures

We present measurements of current noise and cross-correlations in three-terminal Superconductor-Normal metal-Superconductor (S-N-S) nanostructures that are potential solid-state entanglers thanks to Andreev reflections at the N-S interfaces. The noise correlation measurements spanned from the regime where electron-electron interactions are relevant to the regime of Incoherent Multiple Andreev Reflection (IMAR). In the latter regime, negative cross-correlations are observed in samples with closely-spaced junctions.Comment: Include Supplemental Materia

Anatomy of Ursa Majoris

A nearby friable cloud in Ursa Majoris contains 270 galaxies with radial velocities 500 < VLG < 1500 km s^-1 inside the area of RA= [11h; 13h] and DEC= [+40deg; +60deg]. At present, 97 galaxies of them have individual distance estimates. We use these data to clarify the structure and kinematics of the UMa complex. According to Makarov & Karachentsev (2011), most of the UMa galaxies belong to seven bound groups, which have the following median parameters: velocity dispersion of 58 km s^-1, harmonic projected radius of 300 kpc, virial mass of 2.10^12 Msol, and virial- mass-to-K-band-luminosity of 27Msol/Lsol. Almost a half of the UMa cloud population are gas-rich dwarfs (Ir, Im, BCD) with active star formation seen in the GALEX UV-survey. The UMa groups reside within 15-19 Mpc from us, being just at the same distance as Virgo cluster. The total virial mass of the UMa groups is 4.10^13 Msol, yielding the average density of dark matter in the UMa cloud to be Omega_m = 0.08, i.e. a factor three lower than the cosmic average. This is despite the fact that the UMa cloud resides in a region of the Universe that is an apparent overdensity. A possible explanation for this is that most mass in the Universe lies in the empty space between clusters. Herewith, the mean distances and velocities of the UMa groups follow nearly undisturbed Hubble flow without a sign of the 'Z-wave" effect caused by infall toward a massive attractor. This constrains the total amount of dark matter between the UMa groups within the cloud volume.Comment: correction of a typo in the abstract, 18 pages, 2 figures. accepted for MNRAS, nov 26, 201

Giant disk galaxies : Where environment trumps mass in galaxy evolution

We identify some of the most HI massive and fastest rotating disk galaxies in the local universe with the aim of probing the processes that drive the formation of these extreme disk galaxies. By combining data from the Cosmic Flows project, which has consistently reanalyzed archival galaxy HI profiles, and 3.6$\mu$m photometry obtained with the Spitzer Space Telescope, with which we can measure stellar mass, we use the baryonic Tully-Fisher (BTF) relationship to explore whether these massive galaxies are distinct. We discuss several results, but the most striking is the systematic offset of the HI-massive sample above the BTF. These galaxies have both more gas and more stars in their disks than the typical disk galaxy of similar rotational velocity. The "condensed" baryon fraction, $f_C$, the fraction of the baryons in a dark matter halo that settle either as cold gas or stars into the disk, is twice as high in the HI-massive sample than typical, and almost reaches the universal baryon fraction in some cases, suggesting that the most extreme of these galaxies have little in the way of a hot baryonic component or cold baryons distributed well outside the disk. In contrast, the star formation efficiency, measured as the ratio of the mass in stars to that in both stars and gas, shows no difference between the HI-massive sample and the typical disk galaxies. We conclude that the star formation efficiency is driven by an internal, self-regulating process, while $f_C$ is affected by external factors. We also found that the most massive HI detected galaxies are located preferentially in filaments. We present the first evidence of an environmental effect on galaxy evolution using a dynamical definition of a filament.Comment: 14 pages, in press MNRA

The effects of aggregation and protein corona on the cellular internalization of iron oxide nanoparticles

Engineered inorganic nanoparticles are essential components in the development of nanotechnologies. For applications in nanomedicine, particles need to be functionalized to ensure a good dispersibility in biological fluids. In many cases however, functionalization is not sufficient : the particles become either coated by a corona of serum proteins or precipitate out of the solvent. In the present paper, we show that by changing the coating of iron oxide nanoparticles from a low-molecular weight ligand (citrate ions) to small carboxylated polymers (poly(acrylic acid)), the colloidal stability of the dispersion is improved and the adsorption/internalization of iron towards living mammalian cells is profoundly affected. Citrate-coated particles are shown to destabilize in all fetal-calf-serum based physiological conditions tested, whereas the polymer coated particles exhibit an outstanding dispersibility as well as a structure devoid of protein corona. The interactions between nanoparticles and human lymphoblastoid cells are investigated by transmission electron microscopy and flow cytometry. Two types of nanoparticle/cell interactions are underlined. Iron oxides are found either adsorbed on the cellular membranes, or internalized into membrane-bound endocytosis compartments. For the precipitating citrate-coated particles, the kinetics of interactions reveal a massive and rapid adsorption of iron oxide on the cell surfaces. The quantification of the partition between adsorbed and internalized iron was performed from the cytometry data. The results highlight the importance of resilient adsorbed nanomaterials at the cytoplasmic membrane.Comment: 21 pages, 11 figures, accepted at Biomaterials (2011