Abstract

In the decades since I did my PhD at the Cavendish, it has widely been assumed that the basic physics of simple metals is well-understood. Discoveries made over recent years suggest that that assumption was premature. In particular, a growing class of unpurified compounds crystallised using traditional, relatively low-tech methods show huge electron mean free paths. Prominent among these, and featuring the simplest electronic structures, are the metallic layered delafossites PdCoO2, PtCoO2, PdCrO2 and PdRhO2. These are single-band metals and, simultaneouisly, natural heterostructures between strongly – and weakly-correlated layers. Amazingly, they have mean free paths twice as large as elemental silver at room temperature, which grow to tens of microns by 4K. I will review angle resolved photoemission measurements of their bulk and surface electronic structures, and show how the huge resistive mean free paths open the way to electronic viscosity making a significant contribution to their electrical transport properties.