Figure 1: Absorptive pinhole collimators.
From: Absorptive pinhole collimators for ballistic Dirac fermions in graphene
(a) Double pinhole collimator schematic. Current is sourced from bottom contact (red), passes through the bottom aperture and is either absorbed by the top contact (black) or passes into the device bulk. Only trajectories that pass through both apertures reach the bulk, producing a collimated beam. The collimated beam is steered by an external B-field. (b) Optical micrograph of device with four collimators in a Hall-bar-like geometry. Scale bar, 2 μm. (c) Measuring angular distribution. Non-local resistance at n=1.65 × 1012 cm−2 (Fermi wavelength: λf=27.6 nm) is plotted with VS3F3 measured relative to VF1 when current is sourced from both S4 and F4 (blue), and only from S4, whereas F4 is grounded (green). The narrowness of the central peak for the F4-grounded data results from collimation. (d) Theoretical collimation behaviour versus experiment. Left: diagram of effective collimator width w(θ) at a fixed angle for classical ballistic trajectories. Middle: polar plot of theoretical angular dependence for a 300 nm-wide point contact (blue) and a w0=300 nm, L0=850 nm collimator (green). Right: experimental data from c mapped to angle.
