Influence of an impurity on a superconductor/carbon-nanotube/superconductor system

The influence of the impurity on the Andreev bound states and the supercurrents in a superconductor/carbon-nanotube/superconductor system is studied theoretically. The length of the armchair nanotube can cause the on-resonant and off-resonant behaviour of the supercurrent. For the on-resonant case, the impurity suppresses the Andreev bound states and decreases the supercurrents. For the off-resonant case, the impurity induces the Andreev bound states and increases the supercurrents. The supercurrent versus gate voltage shows that the impurity causes the broken of the electron-hole symmetry. The impurity strength effects are also studied.