Quantum oscillations and high carrier mobility in the delafossite   PdCoO$_2$
  We present de Haas-van Alphen and resistivity data on single crystals of the delafossite PdCoO2. At 295 K we measure an in-plane resistivity of 2.6 \mu{\Omega}-cm, making PdCoO2 the most conductive oxide known. The low-temperature in-plane resistivity has an activated rather than the usual T^5 temperature dependence, suggesting a gapping of effective scattering that is consistent with phonon drag. Below 10 K, the transport mean free path is 20 \mum, approximately 10^5 lattice spacings and an astoundingly high value for flux-grown crystals. We discuss the origin of these properties in light of our data. 
Clifford W. Hicks, Alexandra S. Gibbs, Andrew P. Mackenzie, Hiroshi   Takatsu, Yoshiteru Maeno, Edward A. Yelland
cond-mat.str-el