  Room-temperature quasi-ballistic electron transport in double-wall carbon
nanotubes (DWNT) is demonstrated. Conductance dependence on the length was
measured by submerging DWNTs into liquid mercury. The conductance plots show
plateaus, indicating weak dependence of the electrode-tube-electrode electrical
resistance on the length of the connecting nanotube. We infer a mean free path
between 0.6 and 10 micron meters for around 80% of the DWNTs, which is in good
agreement with calculations based on the electron scattering by acoustic
phonons and by disorder.
