Effect of interfacial strain on critical temperature of YBa2Cu3O7-δ thin films

Ultrathin YBa2Cu3O7-delta (YBCO) films down to two unit cells thick have been prepared on LaAlO3 (LAO) and SrTiO3 (STO) substrates for the study of substrate-induced strain effects on critical transition temperature (T-c). The YBCO on LAO has a higher T-c than that on STO for very thin films, and this T-c difference increases with reduction of film thickness. X-ray diffraction experiments reveal that compressive strain exists in the a-b plane for YBCO thin films on LAO, while tensile strain occurs for films on STO. The different stresses in these films account for the T-c difference. (C) 2000 American Institute of Physics. [S0003-6951(00)04423-5].