The transit-time race: ballistic (t ∝ L) versus diffusive (t ∝ L²)  (Datta Sec. 4.1, Eqs. 4.1–4.7)

The gold "bullet" never scatters. The blue electrons are backscattered at random (mean free path λ) and stumble along. Each keeps a stopwatch until it reaches the drain. Datta: t = L/u + L²/2D = t_B(1 + L/λ), and since G = q²D/2t, G = G_Bλ/(L + λ).