Impurity effects on the resonant Andreev reflection in a finite-sized carbon nanotube system

The influence of the impurity on the resonant Andreev reflection through a normal-metal/carbon-nanotube/superconductor system is studied theoretically. It is found that the resonant Andreev reflection depends on the strength of the impurity and the length of the armchair nanotube. The impurity which breaks the electron-hole symmetry of the nanotubes greatly reduces the resonant Andreev reflection. The symmetry broken depends distinctly on the impurity strength. The impurity effects on the Andreev reflection current at different bias are also studied.