Observation of Nonlinear Electrical Transport at the Onset of a Peierls Transition in an Organic Conductor

The $b$-axis conductivity was measured as a function of the electric field $E$ for temperatures $T>\mathrm{}34\mathrm{}$ K in the one-dimensional organic conductor TTF-TCNQ (tetrathiafulvalene-tetracyano-quinodimethane). Deviations from Ohm's law, with a threshold field $E_T$, have been observed for $T<\mathrm{}60\mathrm{}$ K. $E_T$ reaches a minimum of 0.25 V/cm just below the onset of the 54-K Peierls transition before increasing to 6.4 V/cm at 34 K. The results are discussed in terms of the depinning of the charge-density-wave condensate at high fields; the interaction between the two types of chains in TTF-TCNQ is included.