Epitaxy-stabilized n-type superconducting cuprates

We report the growth of n-type superconducting T'-(La,Ce)(2)CuO4 and infinite-layer (IL) (Sr,La)CuO2 thin films by means of molecular beam epitaxy (MBE). The bulk synthesis of T-(La,Ce)(2)CuO4 and IL-(Sr,La)CuO2 requires complicated techniques: synthesis at low temperatures below 600 degreesC for the former and at high pressures above 3 GPa for the latter. This makes it difficult to grow bulk single crystals. We have found, however, that high-quality single-crystalline films of both compounds can be rather easily prepared by thin-film processes. Single-phase T'-(La,Ce)(2)CuO4 films can be obtained for a wide range of x (0.0 less than or equal to x less than or equal to similar to0.4). The best T-c(end) is over 30 K, which is the highest in the T' family. For IL-(SrLa)CuO2, by using KTaO3 substrates, high T-c(end) over 39 K and also metallic resistivity were achieved for the first time to our knowledge. We describe the key parameters in the growth and the properties of the resultant films.