The oxygen isotope effect on critical temperature in superconducting copper oxides

The isotope effect provided a crucial key to the development of the BCS (Bardeen-Cooper-Schrieffer) microscopic theory of superconductivity for conventional superconductors. In Superconducting copper oxides (cuprates) showing an unconventional type of superconductivity, the isotope effect is very peculiar: the exponential coefficient strongly depends on the doping level. No consensus has been reached so far on the origin of the isotope effect in the cuprates. Here we show that the isotope effect in cuprates is in agreement with the bisoliton theory of superconductivity.