Controlling spin wave excitations in magnetic materials underpins the burgeoning field of magnonics. Yet, little is known about how magnons interact with the conduction electrons of itinerant magnets, or how this interplay can be controlled. Via a surface-sensitive spectroscopic approach, we demonstrate a strong and highly-tuneable electron-magnon coupling at the Pd-terminated surface of the delafossite oxide PdCoO2, where a polar surface charge mediates a Stoner transition to itinerant surface ferromagnetism. We show how the coupling can be enhanced 7-fold with increasing surface disorder, and concomitant charge carrier doping, becoming sufficiently strong to drive the system into a polaronic regime, accompanied by a significant quasiparticle mass enhancement. Our study thus sheds new light on electron-magnon interactions in solid-state materials, and the ways in which these can be controlled.
@article{arxiv.2112.04869,
title = {Tuneable electron-magnon coupling of ferromagnetic surface states in PdCoO$_2$},
author = {Federico Mazzola and Chi-Ming Yim and Veronika Sunko and Seunghyun Khim and Pallavi Kushwaha and Oliver J. Clark and Lewis Bawden and Igor Marković and Dibyashree Chakraborti and Timur K. Kim and Moritz Hoesch and Andrew P. Mackenzie and Peter Wahl and Philip D. C. King},
journal= {arXiv preprint arXiv:2112.04869},
year = {2022}
}