"The polar surfaces of the delafossite oxides: from massive Rashba spin-splittings to itinerant surface ferromagnetism"
Who: Federico Mazzola, School of Physics and Astronomy, University of St. Andrews, Scotland, UK
Place: Donostia International Physics Center
Date: Monday, 9 March 2020, 12:00
The ability to manipulate the surface and interface properties of correlated electron systems underpins the burgeoning field of designer quantum matter. Electronic reconstructions arising from polar interfaces have been widely discussed as a way to drastically modify the interface electronic properties of complex oxide heterostructures . Here, we use angle-resolved photoemission spectroscopy (ARPES) to show that an electronic reconstruction occurs at the Pd-terminated polar surfaces of the delafossite oxides, PdCoO2 and PdCrO2. These compounds are wide-band metals in the bulk . We demonstrate how surface doping, as a result of their polarity-driven electronic reconstruction, leads to a massive Rashba spin-splitting for the CoO2 termination  and to a Stoner-instability towards itinerant ferromagnetism for the Pd surface . In particular, I will focus on the Pd termination, where the polarity leads to a ferromagnetic surface atop a non-magnetic bulk in PdCoO2, while in PdCrO2, which is a bulk antiferromagnet, this forms a natural ferromagnetic-antiferromagnetic heterostructure. Our ARPES measurements of the resulting multi-band electronic structures further reveal spectroscopic signatures of a strong and highly tuneable coupling of the surface electrons with magnon-modes. Our work thus paves the way for the creation, control and manipulation of magnetic states at oxide surfaces and in heterostructures, and shows how ARPES is a sensitive probe not only of their surface magnetism, but also coupling with the collective magnetic excitations.
 Hwang et al., Nature Mater. 11, 103 (2012)
Host: Enrique Ortega