Exploring the electronic band structure of individual carbon nanotubes under 60 T

Nano-sciences, and in particular nano-physics, constitute a fascinating world of investigations where the experimental challenges are to synthesize, to address (for instance optically or electrically) to explore and promote the remarkable physical properties of new nano-materials. Somehow, one of the most promising realization of nano-sciences lies in carbon-based nano-materials with sp² covalent bonds. In particular, carbon nanotubes, graphene and more recently ultra-narrow graphene nano-ribbons are envisioned as elementary bricks of the future of nano-electronics. However, prior to such an achievement, the first steps consist in understanding their fundamental electronic properties when they constitute the drain–source channel of a gated device or inter-connexion elements. In this article, we present the richness of challenging experiments combining single-object measurements with an extreme magnetic environment. We demonstrate that an applied magnetic field (B), along with a control of the electrostatic doping, drastically modifies the electronic band structure of a carbon nanotube based transistor. Several examples will be addressed in this presentation. When B is applied parallel to the tube axis, a quantum flux threading the tube induces a giant Aharonov–Bohm conductance modulation mediated by Schottky barriers whose profile is magnetic field dependent. In the perpendicular configuration, the applied magnetic field breaks the revolution symmetry along the circumference and non-conventional Landau states develop in the high field regime. By playing with a carbon nanotube based electronic Fabry–Perot resonator, the field dependence of the resonant states of the cavity reveals the onset of the first Landau state at zero energy. These experiments enlighten the outstanding efficiency of magneto-conductance experiments to probe the electronic properties of carbon based nano-materials. To cite this article: S. Nanot et al., C. R. Physique 10 (2009).     

Superconducting properties of carbon nanotubes

Metallic single wall carbon nanotubes have attracted much interest as 1D quantum wires combining a low carrier density and a high mobility. It was believed for a long time that low temperature transport was exclusively dominated by the existence of unscreened Coulomb interactions leading to an insulating behavior at low temperature. However experiments have also shown evidence of superconductivity in carbon nanotubes. We distinguish two fundamentally different physical situations. When carbon nanotubes are connected to superconducting electrodes, they exhibit proximity induced superconductivity with supercurrents which strongly depend on the transmission of the electrodes. On the other hand intrinsic superconductivity was also observed in suspended ropes of carbon nanotubes and recently in doped individual tubes. These experiments indicate the presence of attractive interactions in carbon nanotubes which overcome Coulomb repulsion at low temperature, and enables investigation of superconductivity in a 1D limit never explored before. To cite this article: M. Ferrier et al., C. R. Physique 10 (2009).     

Multiscale simulation of carbon nanotube devices

In recent years, the understanding and accurate simulation of carbon nanotube-based devices has become very challenging. Conventional simulation tools of microelectronics are necessary to envision the performance and use of nanotube transistors and circuits, but the models need to be refined to properly describe the full complexity of such novel type of devices at the nanoscale. Indeed, many issues such as contact resistance, low dimensional electrostatics and screening effects, as well as nanotube doping or functionalization, demand for more accurate quantum approaches. In this article, we review our recent progress on multiscale simulations which aim at bridging first principles calculations with compact modelling, including the comparison between semi-classical Monte Carlo and quantum transport approaches. To cite this article: C. Adessi et al., C. R. Physique 10 (2009).