Disentangling bulk and surface electronic structure using targeted cleave planes in RuO$_2$

TL;DR

This study uses targeted cleaving and ARPES to distinguish surface and bulk electronic states in RuO$_2$, revealing surface state dominance, spin-orbit effects, and disentangling complex 3D electronic structures.

Contribution

It introduces a method to selectively probe surface electronic states in RuO$_2$ using FIB-engineered cleaves combined with ARPES and theoretical comparison.

Findings

Surface states dominate ARPES spectra of RuO$_2$

Surface termination affects electronic structure

Strong Rashba spin splittings observed due to spin-orbit coupling

Abstract

Rutile RuO$_2$ has attracted significant interest due to its putative unconventional electronic and magnetic properties and its proximity to superconductivity. However, the measurement and interpretation of its electronic structure has been complicated by a strongly three-dimensional crystal structure. Here, we demonstrate how the preparation of targeted $(110)$ and $(100)$ surfaces via focused ion beam (FIB)-engineered cleaving allows the acquisition of high-quality measurements of the electronic structure using angle-resolved photoemission spectroscopy. Our results demonstrate that ARPES spectra of RuO$_2$ are, in fact, largely dominated by signatures of distinct surface electronic states. From comparison with density-functional theory, we resolve a surface termination-dependent variation of these, and disentangle them from highly-three-dimensional bulk states and surface resonances. Moreover, we find a marked role of the substantial spin-orbit coupling of the Ru 4$d$ orbitals in the surface region, where a breaking of spatial inversion symmetry leads to significant Rashba-type spin splittings of the surface bands.