Strain-induced orbital-energy shift in antiferromagnetic <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:msub><mml:mi>RuO</mml:mi><mml:mn>2</mml:mn></mml:msub></mml:math> revealed by resonant elastic x-ray scattering
Benjamin Z. Gregory, J. Strempfer, Daniel Weinstock, Jacob Ruf, Yifei Sun, Hari P. Nair, Nathaniel J. Schreiber, Darrell G. Schlom, Kyle Shen, Andrej Singer
Abstract
In its ground state, ${\mathrm{RuO}}_{2}$ was long thought to be an ordinary metallic paramagnet. Recent neutron and x-ray diffraction revealed that bulk ${\mathrm{RuO}}_{2}$ is an antiferromagnet with ${T}_{N}$ above 300 K. Furthermore, epitaxial strain induces superconductivity in thin films of ${\mathrm{RuO}}_{2}$ below 2 K. Here, we present a resonant elastic x-ray scattering study at the $\mathrm{Ru}\phantom{\rule{0.28em}{0ex}}{L}_{2}$ edge of the strained ${\mathrm{RuO}}_{2}$ films exhibiting the strain-induced superconductivity. We observe an azimuthal modulation of the 100 Bragg peak consistent with bulk. Most notably, in the strained films displaying superconductivity, we observe a $\ensuremath{\sim}1\phantom{\rule{0.28em}{0ex}}\mathrm{eV}$ shift of the $\mathrm{Ru}\phantom{\rule{0.28em}{0ex}}{e}_{g}$ 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.