  An interacting one-dimensional (1D) electron system is predicted to behave
very differently than its higher-dimensional counterparts. Coulomb interactions
strongly modify the properties away from those of a Fermi liquid, resulting in
a Luttinger liquid (LL) characterized by a power-law vanishing of the density
of states at the Fermi level. Experiments on one-dimensional semiconductor
wires and fractional quantum Hall conductors have been interpreted using this
picture, but questions remain about the connection between theory and
experiment. Recently, single-walled carbon nanotubes (SWNTs) have emerged as a
new type of 1D conductor that may exhibit LL behavior. Here we present
measurements of the conductance of individual ropes of such SWNTs as a function
of temperature and voltage. Power law behavior as a function of temperature or
bias voltage is observed: G~ T^a and dI/dV ~ V^a. Both the power-law functional
forms and the inferred exponents are in good agreement with theoretical
predictions for tunneling into a LL.
