Strain-induced orbital energy shift in antiferromagnetic RuO2 revealed by resonant elastic x-ray scattering

TL;DR

This study uses resonant elastic x-ray scattering to reveal how epitaxial strain causes an orbital energy shift in RuO2, linking strain to magnetic and superconducting properties in this complex oxide.

Contribution

It demonstrates the strain-induced orbital energy shift in RuO2 and its relation to superconductivity, providing new insights into strain engineering of complex oxides.

Findings

Strain induces a ~1 eV shift of Ru eg orbitals in RuO2.

Azimuthal modulation consistent with canted AFM observed.

Orbital energy shift varies with film thickness and strain direction.

Abstract

In its ground state, RuO2 was long thought to be an ordinary metallic paramagnet. Recent neutron and x-ray diffraction revealed that bulk RuO2 is an antiferromagnet (AFM) with TN above 300 K. Furthermore, epitaxial strain induces novel superconductivity in thin films of RuO2 below 2 K. Here, we present a resonant elastic x-ray scattering (REXS) study at the Ru L2 edge of the strained RuO2 films exhibiting the strain-induced superconductivity. We observe an azimuthal modulation of the 100 Bragg peak consistent with canted AFM found in bulk. Most notably, in the strained films displaying novel superconductivity, we observe a ~1 eV shift of the Ru eg orbitals to a higher energy. The energy shift is smaller in thicker, relaxed films and films with a different strain direction. Our results provide further evidence of the utility of epitaxial strain as a tuning parameter in complex oxides.