Magnetic electron lensing in the 3D Dirac semi-metal Cd₃As₂

While electrons moving perpendicular to a magnetic field are confined to cyclotron orbits, they can move freely parallel to the field. This simple fact leads to complex current flow in clean, low carrier density semi-metals, such as current jets along the magnetic field when currents pass through point-like constrictions. Occurring accidentally at imperfect current injection contacts, "current jetting" plagues the research of longitudinal magnetoresistance. We demonstrate the controlled generation of tightly focused electron beams in a new class of microdevices machined from crystals of the Dirac semi-metal Cd₃As₂. The current beams can be guided by tilting an in-plane magnetic field and their range tuned by the field strength. Finite element simulations quantitatively capture the voltage induced at faraway contacts when the beams are steered towards them, supporting the picture of controlled electron jets. These experiments demonstrate the first direct control over the highly non-local signal propagation unique to 3D semi-metals in the current jetting regime.