Transport properties of single-wall carbon nanotube Y junctions

Quantum conductivity of a wide class of carbon nanotube Y junctions is calculated using an efficient Green's function embedding scheme. Our results indicate that rectification and switching properties of these junctions depend strongly on the symmetry and to a lesser degree on chirality. We find that a zig-zag tube forming the stem of a symmetric Y junction is sufficient to cause perfect rectification across the junction, otherwise the I-V characteristics remain asymmetric with some leakage current for positive bias voltages. For asymmetric Y junction, on the other hand, we find that no rectification at all is possible. We invoke a model calculation involving Y branching in molecules as well as in nanotubes to explain the dependence of rectification on the nature of the geometry at the branching.