Quantum Interference and Ballistic Transmission in Nanotube Electron Waveguides

The electron transport properties of well-contacted individual single-walled carbon nanotubes are investigated in the ballistic regime. Phase coherent transport and electron interference manifest as conductance fluctuations as a function of Fermi energy. Resonance with standing waves in finite-length tubes and localized states due to imperfections are observed for various Fermi energies. Two units of quantum conductance ${2G}_0{=4e}^2/h$ are measured for the first time, corresponding to the maximum conductance limit for ballistic transport in two channels of a nanotube.