Origin of the kink in the band dispersion of the ferromagnetic perovskite SrRuO3: Electron-phonon coupling

TL;DR

This study investigates the origin of the kink in the band dispersion of SrRuO3, revealing it is primarily due to electron-phonon coupling, especially involving in-plane oxygen phonons, rather than magnetic effects.

Contribution

The paper provides direct experimental evidence linking the band kink in SrRuO3 to electron-phonon interactions, highlighting the role of in-plane phonons across different film thicknesses.

Findings

Kink persists down to 4-unit-cell films.

Negligible change in kink energy with thickness.

Electron-phonon coupling, not magnetic modes, causes the kink.

Abstract

Perovskite SrRuO3, a prototypical conductive ferromagnetic oxide, exhibits a kink in its band dispersion signalling the unusual electron dynamics therein. However, the origin of this kink remains elusive. By taking advantage of the combo of reactive molecular beam epitaxy and in situ angle-resolved photoemission spectroscopy, we systematically studied the evolution of the low-energy electronic structure of SrRuO3 films with thickness thinning down to nearly two-dimensional limit in a well-controlled way. The kink structure persists even in the 4-unit-cell-thick film. Moreover, through quantitative self-energy analysis, we observed the negligible thickness dependence of the binding energy of the kink, which is in sharp contrast to the downward trend of the Curie temperature with reducing the film thickness. Together with previously reported transport and Raman studies, this finding suggests that the kink of perovskite SrRuO3 should originate from the electron-phonon coupling rather than magnetic collective modes, and the in-plane phonons may play a dominant role. Considering such a kink structure of SrRuO3 is similar to these of many other correlated oxides, we suggest the possible ubiquity of the coupling of electrons to oxygen-related phonons in correlated oxides.