Abstract
Recent electrical transport measurements on metallofullerene-doped nanotube peapods are reviewed. In temperature-dependent conductance measurements, it was found that the temperature plays a crucial role in charge transfer between the nanotube and entrapped metallofullerenes and it is shown that the metallofullerenes can function as electron donors and transfer charge to the carbon nanotube host. The amount of charge transferred varies with temperature. At room temperature, the doped nanotube shows p-type conduction. As the temperature decreases, the conductance becomes n-type and even metallic behavior is observed at still lower temperatures, indicating the degenerate state caused by doping.