Why was the isotope effect a hint towards the mechanism of superconductivity?

Question

anonymous · Answer

A) The isotope effect was a direct observation of Cooper pairs.
B) Different isotopes have different types of electrons, which allowed scientists to probe how different kinds of electrons exhibited superconductivity.
C) Different isotopes have the same chemical properties, meaning that their electrons behave more or less the same. Thus, the isotope effect suggested that the lattice ions were important for superconductivity.
D)The isotope effect wasn't a hint towards the mechanism of superconductivity, but rather was the discovery of superconducitivity.