Strategy for accurate thermal biasing at the nanoscale.

We analyze the benefits and shortcomings of a thermal control in nanoscale electronic conductors by means of the contact heating scheme. Ideally, this straightforward approach allows one to apply a known thermal bias across nanostructures directly through metallic leads, avoiding conventional substrate intermediation. We show, by using the average noise thermometry and local noise sensing technique in InAs nanowire-based devices, that a nanoscale metallic constriction on a SiO2 substrate acts like a diffusive conductor with negligible electron-phonon relaxation and non-ideal leads. The non-universal impact of the leads on the achieved thermal bias-which depends on their dimensions, shape and material composition-is hard to minimize, but is possible to accurately calibrate in a properly designed nano-device. Our results allow to reduce the issue of the thermal bias calibration to the knowledge of the heater resistance and pave the way for accurate thermoelectric or similar measurements at the nanoscale.

Direct Observation of a Gate Tunable Band Gap in Electrical Transport in ABC-Trilayer Graphene.

Few layer graphene systems such as Bernal stacked bilayer and rhombohedral (ABC-) stacked trilayer offer the unique possibility to open an electric field tunable energy gap. To date, this energy gap has been experimentally confirmed in optical spectroscopy. Here we report the first direct observation of the electric field tunable energy gap in electronic transport experiments on doubly gated suspended ABC-trilayer graphene. From a systematic study of the nonlinearities in current versus voltage characteristics and the temperature dependence of the conductivity, we demonstrate that thermally activated transport over the energy-gap dominates the electrical response of these transistors. The estimated values for energy gap from the temperature dependence and from the current voltage characteristics follow the theoretically expected electric field dependence with critical exponent 3/2. These experiments indicate that high quality few-layer graphene are suitable candidates for exploring novel tunable terahertz light sources and detectors.

Approaching magnetic ordering in graphene materials by FeCl3 intercalation.

We show the successful intercalation of large area (1 cm(2)) epitaxial few-layer graphene grown on 4H-SiC with FeCl3. Upon intercalation the resistivity of this system drops from an average value of ∼200 Ω/sq to ∼16 Ω/sq at room temperature. The magneto-conductance shows a weak localization feature with a temperature dependence typical of graphene Dirac fermions demonstrating the decoupling into parallel hole gases of each carbon layer composing the FeCl3 intercalated structure. The phase coherence length (∼1.2 µm at 280 mK) decreases rapidly only for temperatures higher than the 2D magnetic ordering in the intercalant layer while it tends to saturate for temperatures lower than the antiferromagnetic ordering between the planes of FeCl3 molecules providing the first evidence for magnetic ordering in the extreme two-dimensional limit of graphene.

Novel highly conductive and transparent graphene-based conductors.

Transparent conductors based on few-layer graphene (FLG) intercalated with ferric chloride (FeCl(3)) have an outstandingly low sheet resistance and high optical transparency. FeCl(3)-FLGs outperform the current limit of transparent conductors such as indium tin oxide, carbon-nanotube films, and doped graphene materials. This makes FeCl(3)-FLG materials the best transparent conductor for optoelectronic devices.