Transition from Sharvin to Drude resistance in high-mobility wires

The resistance of a wire is calculated from the ballistic up to the diffusive transport regime through a semiclassical transmission approach. A formula is derived which describes the transition from the Shravin resistance to the Drude resistance when the mean free path becomes comparable to the wire length. The exact expression differs less than 2.5% from an interpolation formula which simply adds the two resistances. Good agreement with a recent experiment by Tarucha et al. is obtained.