Gate Voltage Controllable Non-Equilibrium and Non-Ohmic Behavior in Suspended Carbon

In this work, we measure the electrical conductance and temperature of individual, suspended quasi-metallic single-walled carbon nanotubes under high voltage biases using Raman spectroscopy, while varying the doping conditions with an applied gate voltage. By applying a gate voltage, the high-bias conductance can be switched dramatically between linear (Ohmic) behavior and nonlinear behavior exhibiting negative differential conductance (NDC). Phonon populations are observed to be in thermal equilibrium under Ohmic conditions but switch to nonequilibrium under NDC conditions. A typical Landauer transport model assuming zero bandgap is found to be inadequate to describe the experimental data. A more detailed model is presented, which incorporates the doping dependence in order to fit this data. The exceptionally strong electron-phonon coupling in quasi-metallic (qm) single-walled carbon nanotubes (SWNTs) leads to exciting low dimensional physics including Kohn anoma-lies,1-5 charge-density waves,6 and Peierls distortions.7 Long mean free paths and high electron velocities make nanotubes an ideal system for studying these interesting effects through high-field, quasi-ballistic electron transport.8 Thermal heating of suspended SWNTs with power densities several hundre