Synthesis and characterization of freestanding Sr₂IrO₄epitaxial thin films

Mott insulating states in Sr₂IrO₄ have attracted substantial interest due to the coexistence of strong spin-orbit interactions and electron correlation. To understand the effect of strain on Sr₂IrO₄, we have synthesized freestanding Sr₂IrO₄ epitaxial thin films. We have deposited Sr₂IrO₄ thin films on water-soluble Sr₃Al₂O₆ buffer layers¹ using pulsed laser deposition. XRD and RSM show that the Sr₃Al₂O₆ buffer layer is strained compressively and Sr₂IrO₄ thin films follow the in-plane lattice constants of the buffer layer. However, the width of rocking curve of freestanding Sr₂IrO₄ thin films is about three times greater than as-grown Sr₂IrO₄ thin films. Also, the in-plane lattice constants of freestanding Sr₂IrO₄ thin films are slightly larger than Sr₂IrO₄ single crystals, presumably due to the introduction of defects during delamination. The optical spectra of freestanding Sr₂IrO₄ thin films show the blue shift of J_eff = ½ interband optical transitions compared to Sr₂IrO₄ thin films grown on SrTiO₃. The blueshift is consistent with the result of tensile strained Sr₂IrO₄ thin films. Freestanding Sr₂IrO₄ thin films offer an opportunity to study their properties under large strain by combining with piezoelectric or mechanical devices.

[1] Di Lu. et al. Nat. Mat. 15, 1255 (2016).