Electronic structure of epitaxially strained Sr₂CrReO₆

Rhenium-based double perovskites (DP) possess rich physics, including magnetic ordering at room temperature, which is a result of an intricate interplay between physical and electronic structure. Among them, Sr₂CrReO₆ (SCRO) stands out due to a high Curie temperature of T_c=620K, a strain-tunable magnetocrystalline anisotropy, and an insulating ground state with a bandgap of 0.21 eV, which can be explained theoretically by orbital ordering.
To characterize orbital ordering, synchrotron x-ray scattering is measured for three strain states of SCRO thin films, compressive (-1%) on a (LaAlO₃)_0.3(Sr₂AlTaO₆)_0.7 (LSAT) substrate, tensile (+1%) on a relaxed SrCr_0.5Nb_0.5O₃ buffer layer on LSAT, and relaxed on SrTiO₃ (STO) substrate. The normally forbidden half-order diffraction peak ((1 1 0.5) in the pseudocubic system) is observed for the unstrained film grown on SrTiO₃, but not for the strained films, which may indicate orbital ordering in the unstrained film. These results will be discussed in light of resonant inelastic x-ray scattering (RIXS) experimental data and calculations.