Super-geometric transverse electron focusing on the hexagonal Fermi surface of PdCoO₂

Single crystals of PdCoO₂ can be easily synthesized at remarkably high quality. At low temperatures, the mean-free-path of this most conductive oxide exceeds 20μm, reflected by its ultra-low residual resistivity of 8 nΩcm. This high conductivity gives rise to different transport regimes, spanning from ballistic transport to hydrodynamic transport regimes. Its ballsitic transport is highly unusual, owing to its peculiar Fermi surface resembling an almost perfect hexagon. We fabricate ballistic structures for transverse electron focusing from as-grown single crystals via focused ion beam machining, and demonstrate magnetic focusing up to 20μm. Compared to typically studied materials with circular Fermi surfaces, the transverse focusing amplitude is strongly enhanced owing to its large parallel sections. We demonstrate this focusing enhancement experimentally, and corroborate it by transport simulations.