Non-equilibrium tunneling spectroscopy in carbon nanotubes

We report measurements of the non-equilibrium electron energy distributions in carbon nanotubes. Carbon nanotubes can be considered model one-dimensional systems whose transport is strongly affected by electron interactions. Using tunneling spectroscopy via a superconducting probe, we have studied electron energy distribution functions, and hence inelastic electron scattering, in nanotubes that have bias voltages applied between their ends. We find that at low temperatures, electrons interact weakly in nanotubes of a few microns channel length, independent of end-to-end conductance values. Surprisingly, the energy relaxation rate can increase substantially when the temperature is raised to only 1.5 K. In general, tunneling spectroscopy with a superconducting probe may be a powerful new tool for characterizing electron behavior in carbon nanotubes.