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.