During the last decade, it has become possible to synthesize and study experimentally artificial atoms, molecules or wires by confining the electron gas in 2 or 3 dimensions.
A natural probe of these systems is the electronic transport. Recently, nanowires, and more specifically carbon nanotubes, have turned out to be particularly interesting for implementing such experiments.
Generally, nanoscale wires are interesting because they allow us to build devices which are model systems for electrons in one or zero dimension. These conductors are currently particularly important in condensed matter. They allow in principle to study coherent manipulation of the quantum state of circuits or strongly correlated electron systems.
In the HQC team, we study experimentally these questions using nanolithography techniques, thin film deposition techniques under UHV, cryogenics as well as microwave measurement techniques.
Most of our experiments make use of carbon nanotubes as building blocks for our devices. Carbon nanotubes are molecular conductors which can be used to explore various aspects of quantum transport. The study of electrical transport leads to couple them to different kinds of metals which have very different properties in general. Single wall carbon nanotubes are naturally one dimensional conductors with four conducting channels (including spin) whereas the electrodes are generally 3D metals. These metals can display various electronic orders (superconducting or ferromagnetic) and are in the weak interaction regime. This is not the case for single wall nanotubes in which strong departures from the physics of non-interacting electrons have been found in the last decade. It is worth mentioning Coulomb blockade, the Kondo effect or the Luttinger liquid physics. A single wall carbon nanotube is therefore the archetype of a hybrid structure where different kinds of electronic orders and/or dimensionalities can be combined.
The potential of single wall nanotubes for implementing various kinds of hybrid structures corresponding to “thought experiments” of quantum transport is illustrated for example by some of the devices which we have studied recently within the HQC team. The first structure is the Cooper pair splitter. The second one is a multiterminal nano spin-valve. The third one is an artificial Kondo impurity.
The study of these three devices relies on the nanofabrication of samples with single wall nanotubes connected to ferromagnets and/or superconductors possibly with high transparency for the contacts. We use for that purpose nanolithography techniques, chemical vapor deposition (CVD) growth and thin film deposition techniques under UHV.