A many-body CPA study of quantum effects in the CMR manganites

A many-body coherent potential approximation (CPA) has been developed for s imple models of the colossal magnetoresistance (CMR) manganites: the double -exchange (DE) and Holstein-DE models. In the classical limit for the local spins and phonons these models are one-electron problems and are exactly s olvable within DMFT. The standard CPA, which is based on getting the atomic limit correct, is equivalent to DMFT for these one-electron problems. We a re interested in the many-body case of quantum local spins and phonons in w hich DMFT must be solved numerically; our extended CPA offers an analytical ly tractable approximate solution of DMFT for this case. We use our CPA to discuss quantum effects on the electronic spectrum, Curie temperature and r esistivity, comparing our results with experiment. Good semi-quantitative a greement is obtained for the temperature and field dependence of the resist ivity. (C) 2001 Elsevier Science B.V. All rights reserved.