Coplanar Al/graphene/Al junctions fabricated on the same graphene sheet deposited on silicon carbide (SiC), show robust Josephson coupling at subKelvin temperature, when the separations between the electrodes is below 400 nm. Remarkably, a hysteretic Critical State sets in when ramping an orthogonal magnetic field, with a sudden collapse of the Josephson critical current Ic when turning the field on, and a revival of Ic when inverting the sweep. Similar hysteresis can be found in granular superconducting films which may undergo the Berezinskii-Kosterlitz-Thouless transition. Here, we give quantitative arguments to prove that this odd behavior of the magnetoconductance gives evidence for an incipient Berezinskii-Kosterlitz-Thouless transition with drift and pinning of fluctuating free vortices induced by the current bias.

We have investigated the disorder of epitaxial graphene close to the charge neutrality point (CNP) by various methods: (i) at room temperature, by analyzing the dependence of the resistivity on the Hall coefficient; (ii) by fitting the temperature dependence of the Hall coefficient down to liquid helium temperature; (iii) by fitting themagnetoresistances at low temperature. All methods converge to give a disorder amplitude of (20±10) meV. Because of this relatively low disorder, close to the CNP, at low temperature, the sample resistivity does not exhibit the standard value~h/4e^2 but diverges. Moreover, themagnetoresistance curves have a unique ambipolar behavior,which has been systematically observed for all studied samples.This is a signature of both asymmetry in the density of states and in-plane charge transfer. The microscopic origin of this behavior cannot be unambiguously determined. However, we propose a model in which the SiC substrate steps qualitatively explain the ambipolar behavior.

We report on the temperature-dependent magnetospectroscopy of two HgTe/CdHgTe quantum wells below and above the critical well thickness dc. Our results, obtained in magnetic fields up to 16 T and s temperature range from 2 to 150 K, clearly indicate a change in the band-gap energy with temperature. A quantum well wider than dc evidences a temperature-driven transition from topological insulator to semiconductor phases. At a critical temperature of 90 K, the merging of inter- and intraband transitions in weak magnetic fields clearly specifies the formation of a gapless state, revealing the appearance of single-valley massless Dirac fermions with a velocity of 5.6×105ms−1. For both quantum wells, the energies extracted from the experimental data are in good agreement with calculations on the basis of the eight-band Kane Hamiltonian with temperature-dependent parameters.

We measure the spin-resolved transport of dipolar excitons in a biased GaAs double quantum well structure. From these measurements we extract both spin lifetime and mobility of the excitons. We find that below a temperature of 4.8K there is a sharp increase in the spin lifetime of the excitons, together with a sharp reduction in their mobility. Below a critical power the spin lifetime increases with increasing mobility and density, while above the critical power the opposite trend is observed. We interpret this transition as evidence of the interplay between two different spin dephasing mechanisms: at low mobility the dephasing is dominated by the hyperfine interaction with the lattice nuclei spins, while at higher mobility the spin-orbit interaction dominates and a Dyakonov-Perel spin relaxation takes over. The excitation power and temperature regime where the hyperfine interaction induced spin dephasing is observed correlates with the regime where a dark dipolar quantum liquid was reported recently on a similar sample.

La prégnance de la dégradation de l’environnement par l’homme doit nous amener à envisager de profonds changements de nos modes de vie, de mobilité, de production et de consommation pour aller vers une humanité plus harmonieuse avec l’environnement. La finalité de la technologie peut servir la résilience écologique.Ainsi, l’avènement d’applications permettant d’envisager un covoiturage dynamique apporterait deux effets bénéfiques à la réduction de la pollution : l’un, lié à une décroissance de la consommation de carburant via l’optimisation du remplissage des véhicules et, l’autre, lié à la diminution du nombre d’automobiles en ville grâce à leur partage.Nous présentons l’embryon d’une application de carsharing reposant sur un algorithme génétique hermaphrodite (actuellement accessible sur github) en espérant pouvoir fédérer des développeurs libres sur le projet

Graphene and AlN are promising materials, interesting to combine together. In this study, we will present first results for direct growth of graphene on bulk AlN and on AlN templates using chemical vapor deposition, including the annealing of these substrates at high temperatures. Atomic force microscopy (AFM) enabled us to study the evolution of the AlN surface morphology after annealing and growth. Few-layer graphene deposition is demonstrated on the basis of X-ray photoemission and Raman spectroscopy

In this work we have carried out variable-load indentation testing on three sodium borosilicate glassesand characterized the indentation imprints using Raman spectroscopy. The resulting analysis of thespectra helps describe the relative amount of densification and shear ow appearing in each glass, as wellas the different microstructural mechanisms that take place during deformation. Additionally, we showthat the two glasses that are relatively poor in sodium exhibit enhanced mixing of the silicate and borateunits after indentation. For the indentations performed using the highest load, we also acquired spectraby focusing at various depths below the imprint, in order to characterize the deformed region of theglasses and estimate its size. Similar experiments have been also carried out for one of the three glassesafter neutron irradiation, in order to study the effects of mechanical deformation on its depolymerizedand swollen structure.