Anomalous isotope effect in low and high T-c superconductors: the contribution of the electronic structure

Some of the low and high T-c superconductors exhibit an anomalous isotope e ffect, where the exponent (alpha) for the isotope effect is much smaller th an 1/2. We present computational results of the electronic structure of sel ected superconductors. The characteristically narrow electron bands of the materials suggest that the rapid variation of their density of states aroun d the Fermi level, within the range of phonon energy, can have a noticeable effect on the total coupling matrix elements. Such effect may explain the anomalous isotope effect on T-c in these materials. (C) 2001 Elsevier Scien ce B.V. All rights reserved.