Epitaxial and Smooth Films of a -Axis YBa 2 Cu 3 O 7

YBa 2 Cu 3 O 7 films have been grown epitaxially on SrTiO 3 (100) and LaAlO 3 (100) substrates with nearly pure a -axis orientation and with transition temperature T c ( R = 0) of 85 K. A unique feature of these films is their smooth surface. These smooth surfaces enable the growth of short-period superlattices with well-defined modulations. The films are untwinned and the grains grow with their c -axis along one of two perpendicular directions on the substrate ([100] or [010]). The fabrication of sandwich-type Josephson junctions with good characteristics may now be possible because unlike c -axis—oriented films, the superconducting coherence length of these smooth films is appreciably large perpendicular to their surfaces.