[en] Ultra-thin films of the conventional superconductors niobium nitride (NbN) and tantalum nitride (TaN) have recently attracted attention for devices such as single-photon detectors. Quasi-optical THz spectroscopy is a particularly suited tool with direct access to superconducting properties, such as the superconducting energy gap, which are necessary for a proper understanding of device performance and for future improvements. With our THz-spectroscopy approach we measure amplitude and phaseshift of coherent radiation (0.09-1.2 THz) passing through thin-film systems. We present the performance and possibilities of our experimental set-up, and we apply it to ultra-thin superconducting films of NbN and TaN. We fit the experimental data to weak-coupling BCS theory, and we obtain frequency- and temperature-dependent superconducting properties such as the complex optical conductivity, the complex dielectric function, the energy gap, the penetration depth, and the superfluid density.

[en] De Haas–van Alphen measurements evidence that oxygen plasma etching strongly affects the properties of the three-dimensional topological insulator Sb_2Te_3. The quantum oscillations in magnetization down to low temperature (T ≥ 2 K) and high magnetic field (B ≤ 7 T) have been systematically investigated using a high-sensitive cantilever torque magnetometer. The effective mass and the oscillation frequency obtained from de Haas–van Alphen measurements first increase and then decrease as the oxygen plasma etching time increases from 0 to 12 min, corresponding to an up- and down-shift of the Dirac point. We establish the cantilever torque magnetometer as a powerful contactless tool to investigate the oxygen sensitivity of the surface state in topological insulators.

[en] This report first gives an overview of the energy system by presenting the determining factors of energy demand and of CO₂ emissions per sector (housing and office building, transport, industry, agriculture, forestry and biomass), by analysing energy systems and CO₂ emissions (energy sources, energy vectors, networks and storage, energy and CO₂ assessment for France), and by describing the guidelines of the scenarios proposed by ANCRE. The three main scenarios are characterized by a stronger sobriety, an electricity-based de-carbonation (with a variant based on nuclear and renewable energies), and diversified vectors. They are notably compared to a trend-based reference scenario. Results are discussed in terms of energy consumption (primary and final energy, consumption by the different sectors), of energy production and CO₂ emissions. Scenarios are assessed in terms of economic, environmental and societal, political and strategic criteria. Some consequences for research topics and funding are identified