Electron spectroscopy of carbon materials: Experiment and theory

We present a comparative spectroscopic study of carbon as graphite, diamond and C60 using C1s K-edge electron energy-loss spectroscopy (EELS), X-ray emission spectroscopy, and theoretical modelling. The first principles calculations of these spectra are obtained in the local density approximation using a self-consistent Gaussian basis pseudo-potential method. Calculated spectra show excellent agreement with experiment and are able to discriminate not only between various carbon hybridisations but also local variation in environment. Core-hole effects on the calculated spectra are also investigated. For the first time, the EEL spectrum of carbyne is calculated

Superfluid stiffness of a KTaO3-based two-dimensional electron gas

After almost twenty years of intense work on the celebrated LaAlO3/SrTiO3 system, the recent discovery of a superconducting two-dimensional electron gases (2-DEG) in (111)-oriented KTaO3-based heterostructures injects new momentum to the field of oxides interfaces. However, while both interfaces share common properties, experiments also suggest important differences between the two systems. Here, we report gate tunable superconductivity in 2-DEGs generated at the surface of a (111)-oriented KTaO3 crystal by the simple sputtering of a thin Al layer. We use microwave transport to show that (111)-KTaO3 2-DEGs exhibit a node-less superconducting order parameter with a gap value significantly larger than expected within a simple BCS weak-coupling limit model. Consistent with the two-dimensional nature of superconductivity, we evidence a well-defined Berezinsky-Kosterlitz-Thouless type of transition, which was not reported on SrTiO3-based interfaces. Our finding offers innovative perspectives for fundamental science but also for device applications in a variety of fields such as spin-orbitronics and topological electronics

Проблематика переходу до інформаційного суспільства

Аналізуються фундаментальні передумови, що є первинними в процесі творення інформаційного суспільства. Обґрунтовується теза, що електронна готовність та електронне залучення є основоположними факторами переходу суспільства від індустріального до інформаційного устрою. Подано основні характеристики цих понять та наголошено на їх значенні

Uncovering latent singularities from multifractal scaling laws in mixed asymptotic regime. Application to turbulence

In this paper we revisit an idea originally proposed by Mandelbrot about the possibility to observe ``negative dimensions'' in random multifractals. For that purpose, we define a new way to study scaling where the observation scale $\tau$ and the total sample length $L$ are respectively going to zero and to infinity. This ``mixed'' asymptotic regime is parametrized by an exponent $\chi$ that corresponds to Mandelbrot ``supersampling exponent''. In order to study the scaling exponents in the mixed regime, we use a formalism introduced in the context of the physics of disordered systems relying upon traveling wave solutions of some non-linear iteration equation. Within our approach, we show that for random multiplicative cascade models, the parameter $\chi$ can be interpreted as a negative dimension and, as anticipated by Mandelbrot, allows one to uncover the ``hidden'' negative part of the singularity spectrum, corresponding to ``latent'' singularities. We illustrate our purpose on synthetic cascade models. When applied to turbulence data, this formalism allows us to distinguish two popular phenomenological models of dissipation intermittency: We show that the mixed scaling exponents agree with a log-normal model and not with log-Poisson statistics.Comment: 4 pages, 3 figure

Nanoscale chemical and structural study of Co-based FEBID structures by STEM-EELS and HRTEM

Nanolithography techniques in a scanning electron microscope/focused ion beam are very attractive tools for a number of synthetic processes, including the fabrication of ferromagnetic nano-objects, with potential applications in magnetic storage or magnetic sensing. One of the most versatile techniques is the focused electron beam induced deposition, an efficient method for the production of magnetic structures highly resolved at the nanometric scale. In this work, this method has been applied to the controlled growth of magnetic nanostructures using Co₂(CO)₈. The chemical and structural properties of these deposits have been studied by electron energy loss spectroscopy and high-resolution transmission electron microscopy at the nanometric scale. The obtained results allow us to correlate the chemical and structural properties with the functionality of these magnetic nanostructures.The authors acknowledge the Spanish Ministry of Science for the financial support through Project No. MAT2008-06567-C02, including FEDER funding, the Aragon Regional Government Grant No. E26. RFP acknowledges F. De la Peña, K. March, and R. Arenal for the scientific discussions. RFP also acknowledges the Spanish Ministry of Science for the funding through a postdoctoral contract

Strain tuning of N el temperature in YCrO3 epitaxial thin films

Epitaxial strain is a useful handle to engineer the physical properties of perovskite oxide materials. Here, we apply it to orthorhombic chromites that are a family of antiferromagnets showing fruitful functionalities as well as strong spin lattice coupling via antisymmetric exchange interaction along Cr O Cr bonds. Using pulsed laser deposition, we grow YCrO3 thin films on various substrates imposing strain levels in the range from amp; 8722;1.8 to 0.3 . The films are stoichiometric with a 3 valence for Cr both within the films and at their surface. They display an antiferromagnetic spin order below their N el temperature, which we show can be strongly tuned by epitaxial strain with a slope of amp; 8722;8.54 K . A dimensionless figure of merit defined as the slope normalized by the N el temperature of bulk is determined to be 6.1, which is larger than that of other perovskites, such as manganites 5.5 , ferrites 2.3 , or nickelates 4.6 . Density functional theory simulations bring insight into the role of Cr O bond lengths and oxygen octahedral rotations on the observed behavior. Our results shed light on orthorhombic chromites that may offer an energy efficient piezo spintronic operatio