Richard L. Greene Dissertation Award in Experimental Condensed Matter or Materials Physics (2020): Delafossite Oxides: natural, ultra-pure metal-insulator heterostructures*

Delafossite oxides are layered compounds, which can be thought of as natural heterostructures of triangularly coordinated metallic sheets and transition metal oxide blocks. A fascinating range of electronic states can be found both in their bulk and on their surfaces, including extremely high conductivity¹ in PtCoO₂ and PdCoO₂, maximal Rashba-like spin-splitting² on the transition metal terminated surfaces of PtCoO₂, PdCoO₂ and PdRhO₂, Stoner ferromagnetism³ on the Pd-terminated surface of PdCoO₂ and, perhaps most remarkably, an intertwined spin-charge response due to a Kondo coupling between metallic and Mott insulating layers⁴ in PdCrO₂. In my PhD I have investigated all of these states experimentally with angle resolved photoemission, and have collaborated with theorists in reaching theoretical understanding of the observed behaviour.
Concentrating on the Rashba-like surface states and the metal/Mott insulator heterostructure, I will show how the simplicity of the materials allows us to pinpoint to the underlying cause for the remarkable electronic behaviour, and in turn to use delafossites as model systems to understand complex phenomena.

¹ Kushwaha, P., Sunko, V. et al., 2015, Sci. Adv. 1, e1500692.
² Sunko, V. et al., 2017, Nature 549, 492
³ Mazzola, F., Sunko, V. et al., 2017., PNAS 51, 12956
⁴ Sunko, V. et al., 2018, Sci. Adv. 6, eaaz0611