Observation of mirror-odd and mirror-even spin texture in ultra-thin epitaxially-strained RuO2 films

TL;DR

This study reveals unconventional mirror-odd and mirror-even spin textures in ultra-thin epitaxially-strained RuO2 films, highlighting strain-induced emergent spin structures distinct from bulk behavior.

Contribution

First experimental observation of mirror-odd and mirror-even spin textures in ultra-thin RuO2, supported by ab-initio calculations and symmetry analysis.

Findings

Unconventional spin texture with mirror-even and mirror-odd components

Symmetry analysis rules out nonmagnetic origins

Epitaxial strain induces emergent non-relativistic spin structure

Abstract

Recently, rutile RuO$_2$ has attracted renewed interest due to expectations of prominent altermagnetic spin-splitting. However, accumulating experimental evidence suggests that in its bulk and thick-film forms, RuO$_2$ does not display any form of magnetic ordering. Despite this, the spin structure of RuO$_2$ remains largely unexplored in the ultra-thin limit, where substrate-imposed epitaxial strain can be substantial. Here, we employ spin-resolved angle-resolved photoemission spectroscopy, supported by ab-initio calculations, to reveal the electronic structure of 2.7~nm-thick epitaxial RuO$_2$ heterostructures. We observe an unconventional spin texture characterized by the coexistence of mirror-even and mirror-odd momentum-dependent components. A comprehensive symmetry analysis rules out nonmagnetic origins of this spin texture. These findings suggest an emergent non-relativistic spin structure enabled by epitaxial strain in the ultra-thin limit, marking a distinct departure from the behavior of relaxed or bulk RuO$_2$. Our work opens new perspectives for exploring symmetry-breaking mechanisms and spin textures in oxide heterostructures.