Superconductivity of Y₁Ba₂(Cu_1-xFe_x)₃O_y

Abstract

A systematic study on the superconductivity of Y 1 Ba 2 (Cu 1- x Fe x ) 3 O y has been made down to 30 mK for various x values. The critical temperature decreases linearly with x . The complete Meissner effect is retained down to 30 mK, up to about x =0.10. The crystal structure of the superconducting phase was found to transform from the orthorhombic to the tetragonal between x =0.02 and 0.05. It is concluded that a branching effect of a one-dimensional chain of Cu1-O through Fe impurities is essential for this structure transition. The supercurrent is considered to flow on the two-dimensional sheets of Cu2.