"Delafossite oxides: natural, ultra-pure metal-insulator heterostructures"

Monday, October 19, 2020

Delafossite oxides are layered compounds, which can be thought of as natural heterostructures oftriangularly coordinated metallic sheetsand transition metal oxide blocks. A fascinating range of electronic statescan be found both in theirbulk andon their surfaces, includingextremely high conductivity1,2in PtCoO2and PdCoO2, maximal Rashba-like spin-splitting3on the transition metal terminated surfaces of PtCoO2, PdCoO2and PdRhO2, Stoner ferromagnetism4on the Pd-terminated surface of PdCoO2and, perhaps most remarkably, an intertwined spin-charge response due to a Kondo couplingbetween metallic and Mott insulating layers5in PdCrO2. Our group hasinvestigated these states experimentally withtransport measurements andangle resolved photoemission, and theoretically with first principles calculationsand model Hamiltonians, where applicable. I willshow how in a number of cases the simplicity and cleanliness of the materials allows us to pinpoint to the underlying cause forthe remarkable electronic behaviour, and in turn to use delafossites as model systems tounderstandcomplex phenomena.

1 Kushwaha, P., Sunko, V., Moll, P.J.W., Bawden, L., Riley, J.M., Nandi, N., Rosner, H., Schmidt, M.P., Arnold, F., Hassinger, E., Kim, T.K., Hoesch, M., Mackenzie, A.P., King,  P.D.C., 2015, Science Advances1, e1500692.
2 Sunko, V.,McGuinness,P.J.,Chang, C. S.,Zhakina, E., Khim, S.,Dreyer,C. E., Konczykowski, M.,Borrmann,H.,Moll,P. J. W., König,M.,Muller,D.A.,Mackenzie.A. P., 2020Physical Review X,10(2):021018.
3 Sunko, V., Rosner, H., Kushwaha, P., Khim, S., Mazzola, F., Bawden, L., Clark, O.J., Riley, J.M., Kasinathan, D., Haverkort, M.W., Kim, T.K., Hoesch, M., Fujii, J., Vobornik, I., Mackenzie, A.P., King, P.D.C., 2017, Nature549, 492
4 Mazzola, F., Sunko, V., Khim, S., Rosner, H., Kushwaha, P., Clark, O.J., Bawden, L., Marković, I., Kim, T.K., Hoesch, M., Mackenzie, A.P., King, P.D.C., 2017., PNAS51, 12956
5 Sunko, V., Mazzola, F., Kitamura, S., Khim, S., Kushwaha, P., Clark, O. J. , Watson, M., Marković, I., Biswas, D., Pourovskii, L., Kim, T. K., Lee, T.-L. ,Thakur, P. K., Rosner, H., Georges, A., Moessner, R., Oka, T.,Mackenzie, A. P., and King, P. D. C., 2020, Science Advances6, eaaz0611.

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Max Planck Institute for Chemical Physics of Solids, Dresden, Germany