Abstract

Electronic transport in metals is typically diffusive and well described by Ohm’s law. Very small or clean conductors, however, can enter the ballistic regime when the mean-free-path exceeds the size of the sample. This transport regime has been well studied in two-dimensional electron gases, in which the charge carriers are well described by small, circular Fermi surfaces.

In the ultra-pure delafossite metal PdCoO2, however, the electronic system is described by a nearly perfect hexagonal Fermi surface, resulting in three preferred directions of ballistic motion. Exploiting the mean-free-path of over 20µm at low temperatures, we use focused ion beam microstructuring to fabricate ballistic devices from single crystals.

I will present our investigations of constricted channels and transverse electron focusing devices which demonstrate the effects of this peculiar Fermi surface. Ballistic transport simulations further corroborate our experimental results. This is particularly relevant in establishing a complete picture of the exotic ballistic motion in PdCoO2, on top of which strong momentum-conserving scattering processes have been argued to lead to hydrodynamic transport.