Shot noise in carbon nanotubes

Abstract

Carbon nanotubes may constitute the ultimate conducting wires for nano-electronics, with their diameters as small as a few tens of atoms and their length of order one micrometer. Because of the particular band structure of graphite, nanotubes have at most two conducting channels, which makes them a one dimensional conductor with very exotic properties. Experimental investigations have indeed shown non conventional features, such as non-ohmic behavior, superconductivity and an ability to carry a huge current density. We have carried out shot noise measurements on nanotubes which are suspended between metallic electrodes. One consequence of the suspended geometry is a very low 1/f noise, thereby enabling the extraction of shot noise. In bundles of nanotubes, we find a reduction of shot noise by more than a factor 100 compared to the full noise 2.e.I expected for uncorrelated electrons. A low noise is also found in an isolated single wall nanotube. In a simple non-interacting-electron picture, such a low shot noise implies that the electrical conduction through a bundle of nanotubes is concentrated in a few ballistic tubes. Another interpretation however would be that a substantial fraction of the tubes conduct with a strong reduction of the effective charge (more than a factor 50) due to electron-electron interaction.