ON THE COMPOSITION-DEPENDENT ISOTOPE EFFECT OF HTSC IN THE 2-BAND MODEL

The oxygen isotope effect in high-T(C) superconductors has been invest igated on the basis of a two-band model where superconducting phase tr ansition is induced by interband (mainly Coulombic) interaction. The i sotope shift of T(C) appears due to the dependence of averaged interba nd electron-phonon coupling constant on oxygen mass. This coupling has a repulsive nature and gives a relatively small contribution to the t otal interaction inducing superconductivity. The calculated isotope ef fect exponent depending on the carrier concentration has been compared with the experimental one as a function of x for La2-xSrxCuO4.