Superconductivity and hybrid soft modes in TiSe2_2

The competition between superconductivity and other ground states of solids is one of the challenging topics in condensed matter physics. Apart from high-temperature superconductors [1,2] this interplay also plays a central role in the layered transition-metal dichalcogenides, where superconductivity is stabilized by suppressing charge-density-wave order to zero temperature by intercalation [3] or applied pressure [4-7]. 1T-TiSe$_2$ forms a prime example, featuring superconducting domes on intercalation as well as under applied pressure. Here, we present high energy-resolution inelastic x-ray scattering measurements of the CDW soft phonon mode in intercalated Cu$_x$TiSe$_2$ and pressurized 1T-TiSe$_2$ along with detailed ab-initio calculations for the lattice dynamical properties and phonon-mediated superconductivity. We find that the intercalation-induced superconductivity can be explained by a solely phonon-mediated pairing mechanism, while this is not possible for the superconducting phase under pressure. We argue that a hybridization of phonon and exciton modes in the pairing mechanism is necessary to explain the full observed temperature-pressure-intercalation phase diagram. These results indicate that 1T-TiSe$_2$ under pressure is close to the elusive state of the excitonic insulator

Saturation and Wilson Line Distributions

We introduce a Wilson line distribution function bar{W}_tau(v) to study gluon saturation at small Feynman x_F, or large tau=ln(1/x_F). This new distribution can be obtained from the distribution W_tau(alpha) of the Color Glass Condensate model and the JIMWLK renormalization group equation. bar{W}_tau(v) is physically more relevant, and mathematically simpler to deal with because of unitarity of the Wilson line v. A JIMWLK equation is derived for bar{W}_tau(v); its properties are studied. These properties are used to complete Mueller's derivation of the JIMWLK equation, though for bar{W}_tau(v) and not W_tau(alpha). They are used to derive a generalized Balitsky-Kovchegov equation for higher multipole amplitudes. They are also used to compute the unintegrated gluon distribution at x_F=0, yielding a completely flat spectrum in transverse momentum squared k^2, with a known height. This is similar but not identical to the mean field result at small k^2.Comment: One reference and two short comments added. To appear in Physical Revies

Enhancement of Hydroxyapatite Dissolution through Krypton Ion Irradiation

International audienceHydroxyapatite (HA) synthesized by a wet chemical route was subjected to heavy ion irradiation, using 4 MeV Krypton ions (Kr 17+) with ion fluence ranging from 1×10 13 to 1×10 15 ions/cm 2. Glancing incidence X-ray diffraction (GIXRD) results confirmed the phase purity of irradiated HA with a moderate contraction in lattice parameters, and further indicated irradiation-induced structural disorder, evident by a broadening of diffraction peaks. High-resolution transmission electron microscopy (HRTEM) observations indicated that the applied Kr irradiation induced significant damage in the hydroxyapatite lattice. Specifically, cavities were observed with their diameter and density varying with irradiation fluences while a radiation-induced crystalline-to-amorphous transition with increasing ion dose was identified. Raman and X-ray photoelectron spectroscopy (XPS) analysis further indicated the presence of irradiation-induced defects. Compositional analysis of pristine and irradiated materials following immersion in Tris (pH 7.4, 37℃) buffer showed that dissolution in vitro was enhanced by irradiation, reaching a peak for 0.1dpa. We examined the effects of irradiation on the early stages of the mouse osteoblast-like cells (MC3T3-E) response. A cell counting kit-8 assay (CCK-8 test) was carried out to investigate the cytotoxicity of samples, and viable cells can be observed on the irradiated materials.L'hydroxyapatite (HA) synthétisée par voie chimique a été soumise à une irradiation ionique lourde, en utilisant des ions Krypton 4 MeV (Kr 17+) avec une fluence ionique allant de 1 × 10 13 à 1 × 10 15 ions / cm 2. Incidence du regard X- Les résultats de la diffraction des rayons (GIXRD) ont confirmé la pureté de phase de l'AH irradié avec une contraction modérée des paramètres du réseau et ont en outre indiqué un trouble structurel induit par l'irradiation, évident par un élargissement des pics de diffraction. Des observations en microscopie électronique à transmission à haute résolution (HRTEM) ont indiqué que l'irradiation au Kr appliquée a induit des dommages importants dans le réseau d'hydroxyapatite. Plus précisément, des cavités ont été observées avec leur diamètre et leur densité variant avec les fluences d'irradiation tandis qu'une transition cristalline-amorphe induite par le rayonnement avec une dose ionique croissante a été identifiée. L'analyse par spectroscopie photoélectronique Raman et X (XPS) a en outre indiqué la présence de défauts induits par l'irradiation. L'analyse de la composition des matériaux vierges et irradiés après immersion dans du tampon Tris (pH 7,4, 37 ℃) a montré que la dissolution in vitro était améliorée par irradiation, atteignant un pic de 0,1 dpa. Nous avons examiné les effets de l'irradiation sur les premiers stades de la réponse des cellules de type ostéoblaste de souris (MC3T3-E). Un test de comptage de cellules kit 8 (test CCK-8) a été réalisé pour étudier la cytotoxicité des échantillons, et des cellules viables peuvent être observées sur les matériaux irradiés

Aperçu nanostructural du comportement en dissolution de l'hydroxyapatite dopée au Sr

International audienceIn this study, high-resolution transmission electron microscopy (HRTEM) was employed to characterize the nanostructure of strontium-substituted hydroxyapatite (Sr-HA) and its evolution following in vitro immersion in physiological solutions. HRTEM images showed that the substitution of Sr induced local distortions in the hydroxyapatite (HA) lattice: minor levels of edge dislocations were detected at low doping contents of Sr ions (1 at %); when the Sr content exceeded 10 at%, the density of grain boundaries increased notably and triple junctions were clearly observed. The dissolution of undoped HA was initiated at crystallite surfaces, whereas the dissolution of Sr-HA started around grain boundaries. Acicular nanocrystal reprecipitation was observed on grain surfaces immersed in simulated body fluid (SBF), while not in dilute hydrochloric acid (HCl). These findings suggest appropriate levels of Sr incorporation can introduce imperfections in the crystal structure of apatite and thus enhance its dissolution rate towards enhanced physicochemical performance in biomedical applicationshttps://doi.org/10.1016/j.jeurceramsoc.2018.07.056Dans cette étude, la microscopie électronique à transmission à haute résolution (HRTEM) a été utilisée pour caractériser la nanostructure de l'hydroxyapatite substituée au strontium (Sr-HA) et son évolution après immersion in vitro dans des solutions physiologiques. Les images HRTEM ont montré que la substitution des distorsions locales induites par le Sr dans le réseau d'hydroxyapatite (HA): des niveaux mineurs de dislocations de bords ont été détectés à de faibles teneurs en dopage d'ions Sr (1 at%); lorsque la teneur en Sr dépassait 10% at%, la densité des joints de grains augmentait de manière notable et des triple jonctions étaient clairement observées. La dissolution de l'HA non dopée a été initiée au niveau des surfaces de cristallites, alors que la dissolution de Sr-HA a commencé autour des joints de grains. Une reprécipitation aciculaire de nanocristaux a été observée sur des surfaces de grains immergées dans un fluide corporel simulé (SBF), mais non dans de l'acide chlorhydrique dilué (HCl). Ces découvertes suggèrent que des niveaux appropriés d’incorporation de Sr peuvent introduire des imperfections dans la structure cristalline de l’apatite et ainsi augmenter sa vitesse de dissolution afin d’améliorer les performances physicochimiques dans les applications biomédicales.https://doi.org/10.1016/j.jeurceramsoc.2018.07.05

Critical Currents of Ideal Quantum Hall Superfluids

Filling factor $\nu=1$ bilayer electron systems in the quantum Hall regime have an excitonic-condensate superfluid ground state when the layer separation $d$ is less than a critical value $d_c$. On a quantum Hall plateau current injected and removed through one of the two layers drives a dissipationless edge current that carries parallel currents, and a dissipationless bulk supercurrent that carries opposing currents in the two layers. In this paper we discuss the theory of finite supercurrent bilayer states, both in the presence and in the absence of symmetry breaking inter-layer hybridization. Solutions to the microscopic mean-field equations exist at all condensate phase winding rates for zero and sufficiently weak hybridization strengths. We find, however, that collective instabilities occur when the supercurrent exceeds a critical value determined primarily by a competition between direct and exchange inter-layer Coulomb interactions. The critical current is estimated using a local stability criterion and varies as $(d_c-d)^{1/2}$ when $d$ approaches $d_c$ from below. For large inter-layer hybridization, we find that the critical current is limited by a soliton instability of microscopic origin.Comment: 18 RevTeX pgs, 21 eps figure

Quantum trajectory approach to stochastically-induced quantum interference effects in coherently-driven two-level atoms

Stochastic perturbation of two-level atoms strongly driven by a coherent light field is analyzed by the quantum trajectory method. A new method is developed for calculating the resonance fluorescence spectra from numerical simulations. It is shown that in the case of dominant incoherent perturbation, the stochastic noise can unexpectedly create phase correlation between the neighboring atomic dressed states. This phase correlation is responsible for quantum interference between the related transitions resulting in anomalous modifications of the resonance fluorescence spectra.Comment: paper accepted for publicatio

Accelerating Neoproterozoic research through scientific drilling

No abstract available

Contributions of gluon recombination to saturation phenomena

Parton distributions in the small $x$ region are numerically predicted by using a modified DGLAP equation with the GRV-like input distributions. We find that gluon recombination at twist-4 level obviously suppresses the rapid growth of parton densities with $x$ decrease. We show that before the saturation scale $Q^2_s$ is reached, saturation and partial saturation appear in the small $x$ behavior of parton distributions in nucleus and free proton, respectively. The antishadowing contributions to the saturation phenomena are also discussed.Comment: 23 pages, LATEX, 22 figures, to appear in Phys. Rev.

Graphene: A Pseudochiral Fermi Liquid

Doped graphene sheets are pseudochiral two-dimensional Fermi liquids with abnormal electron-electron interaction physics. We address graphene's Fermi liquid properties quantitatively using a microscopic random-phase-approximation theory and comment on the importance of using exchange-correlation potentials based on the properties of a chiral two-dimensional electron gas in density-functional-theory applications to graphene nanostructures.Comment: 15 pages, 4 figures, submitte

Continuous-distribution puddle model for conduction in trilayer graphene

An insulator-to-metal transition is observed in trilayer graphene based on the temperature dependence of the resistance under different applied gate voltages. At small gate voltages the resistance decreases with increasing temperature due to the increase in carrier concentration resulting from thermal excitation of electron-hole pairs. At large gate voltages excitation of electron-hole pairs is suppressed, and the resistance increases with increasing temperature because of the enhanced electron-phonon scattering. We find that the simple model with overlapping conduction and valence bands, each with quadratic dispersion relations, is unsatisfactory. Instead, we conclude that impurities in the substrate that create local puddles of higher electron or hole densities are responsible for the residual conductivity at low temperatures. The best fit is obtained using a continuous distribution of puddles. From the fit the average of the electron and hole effective masses can be determined.Comment: 18 pages, 5 figure