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 conductivity in PtCoO₂ and PdCoO₂ [1], maximal Rashba-like spin-splitting on the transition metal terminated surfaces of PtCoO₂, PdCoO₂ and PdRhO₂ [2], Stoner ferromagnetism on the Pd-terminated surface of PdCoO₂ [3] and, perhaps most remarkably, an intertwined spin-charge response due to a Kondo coupling between metallic and Mott insulating layers in PdCrO₂ [4]. Our group has investigated these states experimentally with angle resolved photoemission, and theoretically with first principles calculations and model Hamiltonians, where applicable.
Concentrating on the metal/Mott insulator heterostructure and the Rashba-like surface states, 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, Science Advances 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, arXiv:1809.08972