Superconducting FeSe membrane synthesized by etching of water-soluble Sr3Al2O6 layer

The development of the epitaxial lift-off technique using a pseudoperovskite Sr3Al2O6 sacrificial layer has unleashed latent physical properties emerging in freestanding membranes, mainly composed of lattice-matched perovskite-type complex oxides. Here, we report the superconductivity in a freestanding single-crystalline FeSe membrane prepared using a SrTiO3 capped water-soluble Sr3Al2O6 sacrificial layer, which serves as an ex situ growth template. The FeSe membrane is synthesized by etching the sacrificial layer and transferred on a SiO2/Si substrate. X-ray diffraction pattern and scanning transmission electron microscopy reveal that the FeSe membrane is fully relaxed with minimum degradation of its structural properties during the lift-off process. A superconductivity with zero resistance below 4.2 K is exhibited in the freestanding FeSe membrane, while it is not observed in a compressed thin-film form by an in-plane tensile strain. In addition, critical magnetic field and critical current density of the FeSe membrane are comparable to those of the bulk single crystal. Our demonstration of the superconducting FeSe membrane ensures a high utility of the epitaxial lift-off technique for various thin-film materials grown on SrTiO3. This study paves the way for functional applications using ex situ thin-film growth and lift-off technique with an expanded selection from an inventory of various materials.