We have obtained a REBa2Cu3O7-y (RE=rare earth element) superconducting single-crystal thin film on a MgO (100) substrate using a magnetron sputtering method. For a HoBa2Cu3O7-y thin film, we obtained a Jc of more than 3×106A/cm2 at the temperature of liquid nitrogen, and the deterioration of the magnetic field was far less than that for sintered bulk material. Through X-ray diffraction, it was confirmed that the growth of the c axis was perpendicular to the substrate. In addition, reflection high energy electron diffraction and observation with a high resolution scanning electron microscope confirmed that the surface was extremely smooth and flat. This is a great improvement in comparison with the poly-crystal film (with a Jc of 104 to 105A/cm2) which was previously reported, and it is expected that this can open the way for applications in electronics fields which require a Jc of 106A/cm2 or higher.
