SIGNIFICANT IMPROVEMENT OF SUPERCONDUCTIVITY OF LASER-ABLATED YBA2CU3O7/MGO THIN-FILMS - INTRODUCTION OF A SRTIO3 BUFFER LAYER

Laser ablated thin films of YBa2Cu3O7 on a MgO substrate using a SrTiO3 buffer layer have been grown. The 250 Angstrom thick film of SrTiO3 is perfectly oriented with respect to the MgO substrate with [100](STD)//[100](MgO), in spite of the mismatch between the two lattices parameters. The SrTiO3 film is well crystallized and only rare defects are observed, located near the interface with MgO. The deposition of YBa2Cu3O7 on the SrTiO3 film is epitaxial:the YBa2Cu3O7 film, that is about 2000 Angstrom thick, exhibits only one kind of orientation with respect to MgO:[100](YBCO) or [010](YBCO)//[100](STO)//[100](MgO). Superconductivity is improved in a spectacular manner with respect to YBa2Cu3O7 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 YBa2Cu3O7 films deposited on a SrTiO3 substrate, open the route to the use of MgO substrate for microwave applications.