EPITAXIAL AND SMOOTH FILMS OF A-AXIS YBA2CU3O7

YBa2Cu3O7 films have been grown epitaxially on SrTiO3 (100) and LaAlO3 (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.