Isotope shift exponent in two-band high-Tc superconductors with linear-energy-dependent electronic density of states

The isotope shift exponent is derived from the two-band BCS gap equation with a Linear-energy-dependent electronic density of states and assuming that both the electron-phonon and free-carrier negative-U centre interacting mechanisms are simultaneously present. The result shows that some of the anomalous features of the isotope shift exponent observed in high-T-c superconductors could be interpreted within this present model. (C) 1999 Elsevier Science B.V. All rights reserved.