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

In the ruthenium perovskite family, epitaxial strain has been shown to enhance magnetization and tune T_c in superconductors. Recently strain engineering has been shown to induce superconductivity in the previously non-superconducting metal RuO₂. Long thought to be an ordinary, paramagnetic metal, neutron and x-ray diffraction have revealed a surprising antiferromagnetic ground state in RuO₂ . Here we present a magnetic resonant x-ray scattering (RXS) study of the same RuO₂ film specimens used to demonstrate strain-induced superconductivity. At the Ru L₂ edge we can access the forbidden magnetic reflection (100) and probe the magnetic ground state, domain sizes and electronic properties. We notably observe a large, strain-dependent shift of Ru e_g orbitals to higher energy in the sample that hosts novel superconductivity.