Localized states in metallic carbon nanotube systems

W. Jaskólski Instytut Fizyki, Uniwersytet Miko laja Kopernika, Grudzia̧dzka 5, 87-100 Toruń, Poland Abstract We have found that purely metallic carbon nanotubes consisting of a nanometer-size metallic island connected to another two metallic nanotubes by topological defects, may present discrete energy levels, thus behaving as metallic quantum dots. When there is a symmetry gap around the Fermi energy between the matched tubes, the states are strongly localized in the central metallic section and are completely uncoupled from the outer leads. This results into a conductance gap for a wide energy window. Remarkably, we also find discrete levels in structures made of metallic nanotubes without a common symmetry. In this case the states are actually resonances coupled to the leads continua. Such coupling is responsible for the non-zero conductance at the energies of the resonant states, yielding interesting transport characteristics that may be exploited for carbon nanotube single electron transistors.