An unusual form of superconducting transition has been observed in some of the superconducting compounds ${\mathit{L}}_{2\mathrm{-}\mathit{x}}$${\mathit{M}}_{\mathit{x}}$${\mathrm{CuO}}_{4\mathrm{-}\mathit{y}}$ (L=Pr,Nd,Sm,Eu; M=Ce,Th) under low magnetic fields. When the temperature is reduced below the critical one, the sample’s resistance first increases, then drops to a nonzero value, increases again, and finally decreases at low temperature, creating a characteristic double-peak transition. The behavior is explained in terms of intra- and intergranular superconducting transitions.

• Received 25 June 1990

DOI:https://doi.org/10.1103/PhysRevLett.65.3201