Signatures of phase coherence in the low-temperature transport properties of multiwall carbon nanotubes

Four-terminal low-temperature measurements of the electrical transport of multiwall carbon nanotube devices with low-resistance contacts reveal features that signify the presence of phase coherent transport. Sharp resonances in the differential resistance as a function of dc bias are observed that are due to the interference of electron paths that are directly transmitted through the nanotube and paths that are transmitted via resonant states, the so-called Fano resonance. The metastability of these resonances indicates that the resonant states most likely arise from potentials created by metastable defects in the device. Correlations between the nanotube conductance and the simultaneously measured conductance of the contacts hint that the defects may be located at the contacts, although the nonlocality introduced by the long-range phase coherence makes an absolute determination of the location of the impurities by this technique impossible.