Nonlinear Response of a Clean One-Dimensional Wire

We study nonlinear transport in a clean one-dimensional wire fabricated by cleaved edge overgrowth in molecular beam epitaxy. At low electron densities, and with a large applied bias, we observe a feature in the differential conductance similar to the so-called ``0.7 structure,'' found in quantum point contact devices. Using a simple model we suggest a link between this phenomenon, charge neutrality, and unidirectional dynamics in the wire.