Polarons and isotope effect in manganites

Numerical estimates are carried out which show that the polaronic effects c annot be an origin of specific properties of the CMR materials. A quantum-m echanical calculation of the charge carrier band narrowing with increasing temperature is carried out for the double-exchange systems. Comparing its r esults with experimental data shows that the hole-phonon coupling in them i s too weak for the small polaron formation. Despite this, a giant isotope e ffect is possible in the manganites due to an isotope dependence of the non stoichiometry of manganites. to which lattice vibrations contribute conside rably. (C) 1999 Published by Elsevier Science B.V. All rights reserved.