Significant improvement of superconductivity of laser ablated “YBa2Cu3O7/MgO” thin films: introduction of a SrTiO3 buffer layer

Abstract Laser ablated thin films of YBa 2 Cu 3 O 7 on a MgO substrate using a SrTiO 3 buffer layer have been grown. The 250 A thick film of SrTiO 3 is perfectly oriented with respect to the MgO substrate with [100] STO / /[100] MgO , in spite of the mismatch between the two lattices parameters. The SrTiO 3 film is well crystallized and only rare defects are observed, located near the interface with MgO. The deposition of YBa 2 Cu 3 O 7 on the SrTiO 3 film is epitaxial: the YBa 2 Cu 3 O 7 film, that is about 2000 A thick, exhibits only one kind of orientation with respect to MgO: [100] YBCP or [010] YBCO / /[100] STO / /[100] MgO . Superconductivity is improved in a spectacular manner with respect to YBA 2 Cu 3 O 7 directly deposited on MgO. A critical temperature T c ( R = 0) of 92 K and a critical current density of 4.10 6 A/cm 2 at 82 K are reached for the first time for films deposited on MgO substrate. These characteristics, similar to those of YBa 2 Cu 3 O 7 films deposited on a SrTiO 3 substrate, open the route to the use of MgO substrate for microwave applications.