Is the Isotope Effect Absent in YB sub 2-Cu sub 3 O sub (7- delta) - Reply

The mechanism responsible for the high-temperature superconductivity in the recently discovered metallic oxides is the key theoretical issue in this field at the present time. For this reason the presence or absence of an isotope effect is extremely important since it provides a clue as to whether the conventional mechanism for superconductivity can be discarded. In two recent articles [1,2] it was reported that the substitution of the isotope sup 18 O in YBa sub 2 Cu sub 3 O sub (7-delta) prepared with sup 16 O has no perceptible effect on the superconducting transition.