ELECTRON LOCALIZATION IN MIXED-VALENCE MANGANITES

Mixed-valence manganites (A(0.7)(3+)B(0.3)(2+))MnO3 exhibit a resistivity peak with giant negative magnetoresistance below the Curie point. Residual resistivity ranges from 5 X 10(-8) to 8 X 10(3) Omega m, but the electronic heat capacity when A = Y or La is that of a normal d-band metal; y approximate to 6 mJ mole(-1) K-2 Spatial fluctuations in the Coulomb and spin-dependent potentials localize the e(g) up arrow (sigma*) electrons in wave packets that are large on the scale of the Mn-Mn separation. Transport in the magnetically localized state involves zero-point-energy assisted hopping or tunneling of electrons from one weakly localized wave packet to another.