Negative differential resistance of carbon nanotube electrodes with asymmetric coupling phenomena

An intricate problem in molecular electronics is to control the molecule-electrodes contacts. Asymmetric couplings between both contacts are important in driving novel nonlinear transport characteristics like negative differential resistance (NDR). We find that in the presence of an applied field, metallic carbon nanotubes (CNTs) can form asymmetric couplings even if symmetric structures are employed. This origin is due to the CNT itself, while the NDR phenomenon can be obtained by tuning the threshold voltage for the asymmetric couplings by a proper choice of a molecule.