Four-terminal resistance of a ballistic quantum wire

The electrical resistance of a conductor is intimately related to the relax ation of the momentum of charge carriers. In a simple model, the accelerati ng force exerted on electrons by an applied electric field is balanced by a frictional force arising from their frequent collisions with obstacles suc h as impurities, grain boundaries or other deviations from a perfect crysta lline order(1). Thus, in the absence of any scattering, the electrical resi stance should vanish altogether. Here, we observe such vanishing four-termi nal resistance in a single-mode ballistic quantum wire. This result contras ts the value of the standard two-probe resistance measurements of h/2e(2) a pproximate to 13 k Omega. The measurements are conducted in the highly cont rolled geometry afforded by epitaxial growth onto the cleaved edge of a hig h-quality GaAs/AlGaAs heterostructure. Two weakly invasive voltage probes a re attached to the central section of a ballistic quantum wire to measure t he inherent resistance of this clean one-dimensional conductor.