Electronic structure of CMR oxides: high resolution electron-spectroscopic studies and a pseudogap

We review our measurements of the electronic structure of the CMR oxides, with special emphasis on high resolution ARPES studies of the Fermi surface and near-E-F states of the layered materials. While the data show many similarities to band theory predictions, there are also critical differences, in particular there being a spectral depletion or pseudogap at E-F. This pseudogap is strongly temperature dependent, with major changes at the sample's T-c. These changes correlate so well with the observed resistive trends that the pseudogap should be considered as a key mechanism cooperating with double-exchange to produce the metal-insulator transition and the CMR effect. We argue that the pseudogap likely originates from strongly fluctuating charge/orbital ordering tendencies. (C) 2001 Published by Elsevier Science B.V.