  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 long-ranged current jets forming along the magnetic field when currents pass
through point-like constrictions. Occurring accidentally at imperfect current
injection contacts, the phenomenon of "current jetting" plagues the research of
longitudinal magneto-resistance which is particularly important in topological
conductors. Here we demonstrate the controlled generation of tightly focused
electron beams in a new class of micro-devices machined from crystals of the
Dirac semi-metal Cd3As2. The current beams can be guided by tilting a 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 nonlocal
signal propagation unique to 3D semi-metals in the current jetting regime, and
may lead to novel applications akin to electron optics in free space.
