The role of hydrogen in room-temperature ferromagnetism at graphite surfaces

We present a x-ray dichroism study of graphite surfaces that addresses the origin and magnitude of ferromagnetism in metal-free carbon. We find that, in addition to carbon $\pi$ states, also hydrogen-mediated electronic states exhibit a net spin polarization with significant magnetic remanence at room temperature. The observed magnetism is restricted to the top $\approx$10 nm of the irradiated sample where the actual magnetization reaches $\simeq 15$ emu/g at room temperature. We prove that the ferromagnetism found in metal-free untreated graphite is intrinsic and has a similar origin as the one found in proton bombarded graphite.Comment: 10 pages, 5 figures, 1 table, submitted to New Journal of Physic

On rationality of the intersection points of a line with a plane quartic

We study the rationality of the intersection points of certain lines and smooth plane quartics C defined over F_q. For q \geq 127, we prove the existence of a line such that the intersection points with C are all rational. Using another approach, we further prove the existence of a tangent line with the same property as soon as the characteristic of F_q is different from 2 and q \geq 66^2+1. Finally, we study the probability of the existence of a rational flex on C and exhibit a curious behavior when the characteristic of F_q is equal to 3.Comment: 17 pages. Theorem 2 now includes the characteristic 2 case; Conjecture 1 from the previous version is proved wron

Observation of Spin-glass-like Behavior in SrRuO3 Epitaxial Thin Films

We report the observation of spin-glass-like behavior and strong magnetic anisotropy in extremely smooth (~1-3 \AA) roughness) epitaxial (110) and (010) SrRuO3 thin films. The easy axis of magnetization is always perpendicular to the plane of the film (unidirectional) irrespective of crystallographic orientation. An attempt has been made to understand the nature and origin of spin-glass behavior, which fits well with Heisenberg model.Comment: 5 pages, 5 Figure

Enhanced electron-phonon coupling in graphene with periodically distorted lattice

Electron-phonon coupling directly determines the stability of cooperative order in solids, including superconductivity, charge and spin density waves. Therefore, the ability to enhance or reduce electron-phonon coupling by optical driving may open up new possibilities to steer materials' functionalities, potentially at high speeds. Here we explore the response of bilayer graphene to dynamical modulation of the lattice, achieved by driving optically-active in-plane bond stretching vibrations with femtosecond mid-infrared pulses. The driven state is studied by two different ultrafast spectroscopic techniques. Firstly, TeraHertz time-domain spectroscopy reveals that the Drude scattering rate decreases upon driving. Secondly, the relaxation rate of hot quasi-particles, as measured by time- and angle-resolved photoemission spectroscopy, increases. These two independent observations are quantitatively consistent with one another and can be explained by a transient three-fold enhancement of the electron-phonon coupling constant. The findings reported here provide useful perspective for related experiments, which reported the enhancement of superconductivity in alkali-doped fullerites when a similar phonon mode was driven.Comment: 12 pages, 4 figure

Stepwise Adsorption of Alkoxy-Pyrene Derivatives onto a Lamellar, Non-Porous Naphthalenediimide-Template on HOPG

The development of new strategies for the preparation of multicomponent supramolecular assemblies is a major challenge on the road to complex functional molecular systems. Here we present the use of a non-porous self-assembled monolayer from uC33-NDI-uC33, a naphthalenediimide symmetrically functionalized with unsaturated 33 carbon-atom-chains, to prepare bicomponent supramolecular surface systems with a series of alkoxy-pyrene (PyrOR) derivatives at the liquid/HOPG interface. While previous attempts at directly depositing many of these PyrOR units at the liquid/HOPG interface failed, the multicomponent approach through the uC33-NDI-uC33 template enabled control over molecular interactions and facilitated adsorption. The PyrOR deposition restructured the initial uC33-NDI-uC33 monolayer, causing an expansion in two dimensions to accommodate the guests. As far as we know, this represents the first example of a non-porous or non-metal complex-bearing monolayer that allows the stepwise formation of multicomponent supramolecular architectures on surfaces

All-optical four-state magnetization reversal in (Ga,Mn)As ferromagnetic semiconductors

Using density matrix equations of motion and a tight-binding band calculation, we predict all-optical switching between four metastable magnetic states of (III,Mn)As ferromagnets. This switching is initiated non-thermally within 100fs, during nonlinear coherent photoexcitation. For a single optical pulse, magnetization reversal is completed after $\sim$100 ps and controlled by the coherent femtosecond photoexcitation. Our predicted switching comes from magnetic nonlinearities triggered by a femtosecond magnetization tilt that is sensitive to un--adiabatic light--induced spin interactions.Comment: 3 pages, 2 figures, submitted in Applied Physics Letter

Direct Observation of Site-specific Valence Electronic Structure at Interface: SiO2/Si Interface

Atom specific valence electronic structures at interface are elucidated successfully using soft x-ray absorption and emission spectroscopy. In order to demonstrate the versatility of this method, we investigated SiO2/Si interface as a prototype and directly observed valence electronic states projected at the particular atoms of the SiO2/Si interface; local electronic structure strongly depends on the chemical states of each atom. In addition we compared the experimental results with first-principle calculations, which quantitatively revealed the interfacial properties in atomic-scale.Comment: 4 pages, 3 figure

Repeated Detection of an Invertebrate Iridovirus (IIV) in Amphibians

Invertebrate iridoviruses (IIVs) (family: Iridoviridae) are known pathogens for invertebrates, causing high mortality and reduced fertility in affected insects. Over the past 2 decades, IIVs have also been increasingly found in lizards in association with nonspecific clinical signs. It has been hypothesized that IIVs from insects can also infect reptiles. From 2010-2011, IIVs were repeatedly detected via polymerase chain reaction testing and virus isolation methods in routine diagnostic samples from different amphibians: 3 blue poison dart frogs (Dendrobates tinctorius azureus), 4 edible frogs (Pelophylax kl. esculentus), a giant ditch frog (Leptodactylus fallax), an Amazon milk frog (Trachycephalus resinifictrix), mixed organs from agile frogs (Rana dalmatina), a black-spined toad (Bufo melanostictus), and one Lake Urmia newt (Neurergus crocatus). IIVs were found in skin swabs from apparently healthy animals, as well as in multiple organs of frogs that died of unknown causes. Prey insects (crickets) from one owner also tested positive for the presence of IIV. The obtained partial sequences from the major capsid protein (MCP) gene (222nt) from each of these were 100% identical to each other and 98% identical to IIV-6, the type species of the genus Iridovirus. Although the pathogenicity of IIV in amphibians remains unclear, these findings provide further evidence that IIVs may be able to infect vertebrates under some conditions and underline the importance of the genus Iridovirus in vertebrates