a-axis growth of YBa2Cu3O7 thin films on LaAlO3 induced by monolayer buffers of PrO2

The deposition of an intermediate buffer of praseodymium oxide (PrO2) of only monolayer thickness (about 2 Å) in a two-temperature process results in the growth of almost exclusive epitaxial a-axis oriented YBa2Cu3O7 (YBCO) on LaAlO3 (100). Under identical experimental conditions, but without the monolayer of PrO2, epitaxial c-axis oriented YBCO films with a critical temperature Tc of 86 K and a transition width of 1 K are obtained. Critical temperatures of these a-axis oriented films are typically 10 K lower than those of the c-axis oriented films. Our findings suggest that a single layer of PrBa2Cu3O7 is formed at the interface, inducing a-axis growth throughout the whole YBCO film.