Measurement of the resistance induced by a single atomic impurity on a (7,6) semiconducting carbon nanotube: scattering strength of individual potassium atoms as a function of gate voltage*

Despite many years of research, no measurements have been performed to determine resistance induced by impurities in carbon nanotubes. Over the last few years, we have developed a capability to measure the resistance induced by a single impurity atom on nanotubes with known chirality. Using this capability, we measured the resistance induced by an individual potassium atom on a (7,6) semiconducting carbon nanotube. The ``atomic'' resistance of potassium is found to be in the kohm range and has a strong dependence on the applied gate voltage. The scattering strength of the p-type (valence band) channel is approximately 20 times greater than that of the n-type (conduction band) channel. We integrate our atomically-controlled experimental result to a numerical recursive Green's function technique, which can precisely model the experiment, to understand the measured ``atomic'' resistance and the asymmetry.