An essential prerequisite to this common transport regime is a momentum-relaxing mean-free path, λ, that is much smaller than the size of the conductor. These results suggest a novel class of ballistic electronic devices exploiting the unique transport characteristics of strongly faceted Fermi surfaces.Įlectronic conduction in metals is typically well captured by Ohm’s law as frequent collisions of the electrons lead to diffusive motion and locally defined conductivity. This super-geometric focusing can be quantitatively predicted for arbitrary device geometry, based on the hexagonal cyclotron orbits appearing in this material. The peculiar hexagonal Fermi surface naturally leads to enhanced electron self-focusing effects in a magnetic field compared to circular Fermi surfaces.
We probe this directional ballistic regime in a single crystal of PdCoO 2 by use of focused ion beam (FIB) micro-machining, defining crystalline ballistic circuits with features as small as 250 nm. Here we demonstrate that the nearly perfectly hexagonal Fermi surface of PdCoO 2 gives rise to highly directional ballistic transport. Currently, this is realized mainly in 2D materials characterized by circular Fermi surfaces. Geometric electron optics may be implemented in solids when electron transport is ballistic on the length scale of a device.
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