The experimental data in Fig. 61 ar

The experimental data in Fig. 61 are compared with the result327 from a numerical simulation of classical trajectories of the electrons at the Fermi level (following the method of Ref.329). This semiclassical calculation was performed in order to relax the assumption of adiabatic transport in the point contact region, and of small Td/N, on which Eqs. (3.32) and (3.34) are based. The dashed curve is for point contacts defined by hardwall contours with straight corners (no collimation); the dots are for the smooth hardwall contours shown in the inset, which lead to collimation via the horn effect (cf. Fig. 60b; the barrier collimation of Fig. 60a is presumably unimportant at the small gate voltage used in the experiment and is not taken into account in the numerical simulation). The angular injection distributions P(α) that follow from these numerical simulations are compared in Fig. 62 (solid histogram) with the result (3.31) from the adiabatic approximation for f = 1.85 (dotted curve). The uncollimated distribution P(α) = (cos α)/2 is also shown for comparison (dashed curve). Taken together, Figs. 61 and 62 unequivocally demonstrate the importance of collimation for the transport properties, as well as the adequateness of the adiabatic approximation as an estimator of the collimation cone.