SUPERCONDUCTIVITY IN THIN-FILMS OF THE COMPOSITION M(0.5)CA(0.5)BA(2)CU(3)O(7-DELTA) (M=LU, TB, TH)

We have grown in situ by laser ablation thin films of the composition M(0.5)Ca(0.5)Ba(2)CU(3)O(7-delta) (M=LU, Tb, Th). The significance of these investigations is that the compositions MBa(2)Cu(3)O(7-delta) (M = Lu, Tb, Th) do not form in single phase in bulk form and, in the case of Tb and Th, not even in thin film form. With partial replacement of the M element by Ca, we are able to grow thin films that are highly crystalline and preferentially oriented. Superconducting transition temperature of the films varies from congruent to 12 K to g 45 K. To the best of our knowledge, these are the first results reporting superconductivity in a 5f-element-based copper oxide system (in this case, M=Th)