Long-range magnetic reconstruction of <i>J</i>_eff = 1/2 pseudospins in Sr₂IrO₄ via 5<i>d</i>-4<i>d</i> interfacial interactions with Sr₂RuO₄

Sr₂IrO₄ has attracted attention for its relativistic Mott insulating states originating from strong spin-orbit coupling (SOC) and electron-correlation. The strong SOC in iridates entangles the magnetic moments and orbital degrees of freedom, making the system sensitive to external stimuli.
We report the magnetic properties of Sr₂IrO₄ driven by 5d-4d interfacial interactions with Sr₂RuO₄. We have synthesized Sr₂IrO₄ thin films on Sr₂RuO₄ single crystal substrates by pulsed laser deposition. This heterostructure has never been studied before. We have observed the magnetic properties of this heterostructure are distinct from Sr₂IrO₄ thin-films under similar strain (-0.5 %) and Sr₂IrO₄ bulk crystals. Resonant inelastic x-ray scattering has revealed an anisotropic softening of magnetic excitations in the Sr₂IrO₄/Sr₂RuO₄, where the modified magnon dispersion indicates enhanced longer-range interactions between the J_eff = 1/2 pseudospins of Sr₂IrO₄. Note that this long-range magnetic reconstruction occurs throughout the entire Sr₂IrO₄. Our results imply the strong interfacial interactions between 5d iridates and 4d ruthenates. The approach of synthesizing epitaxial thin films on unconventional single crystal substrates opens a new direction of studying strongly correlated systems.