Strain engineering of the charge and spin-orbital interactions in SrIrO.

In the high spin-orbit-coupled SrIrO, the high sensitivity of the ground state to the details of the local lattice structure shows a large potential for the manipulation of the functional properties by inducing local lattice distortions. We use epitaxial strain to modify the Ir-O bond geometry in SrIrO and perform momentum-dependent resonant inelastic X-ray scattering (RIXS) at the metal and at the ligand sites to unveil the response of the low-energy elementary excitations. We observe that the pseudospin-wave dispersion for tensile-strained SrIrO films displays large softening along the [h,0] direction, while along the [h,h] direction it shows hardening. This evolution reveals a renormalization of the magnetic interactions caused by a strain-driven cross-over from anisotropic to isotropic interactions between the magnetic moments. Moreover, we detect dispersive electron-hole pair excitations which shift to lower (higher) energies upon compressive (tensile) strain, manifesting a reduction (increase) in the size of the charge gap. This behavior shows an intimate coupling between charge excitations and lattice distortions in SrIrO, originating from the modified hopping elements between the t orbitals. Our work highlights the central role played by the lattice degrees of freedom in determining both the pseudospin and charge excitations of SrIrO and provides valuable information toward the control of the ground state of complex oxides in the presence of high spin-orbit coupling.