On the composition-dependent isotope effect of HTSC in the two-band model

The oxygen isotope effect in high-Tc superconductors has been investigated on the basis of a two-band model where superconducting phase transition is induced by interband (mainly Coulombic) interaction. The isotope shift of Tc appears due to the dependence of averaged interband electron-phonon coupling constant of oxygen mass. This coupling has a repulsive nature and gives a relatively small contribution to the total interaction inducing superconductivity. The calculated isotope effect exponent depending in the carrier concentration has been compared with the experimental one as a function of x for La2-xSrxCuO4. (orig.)