Coexistence of large and small polarons in manganites - art. no. 052406

The interplay of the electron-phonon interaction and of the double- and sup erexchange magnetic effects is analyzed in the La1-xCaxMnO3 perovskites wit h 0<x<0.5. By using an analytical variational scheme that allows us to trea t the electron-phonon interaction in a fully quantum manner it is shown tha t in the intermediate electron-phonon coupling regime a charge-density inst ability occurs near the metal-insulator transition, induced by either tempe rature or hole doping. The system segregates in antiferromagnetic or parama gnetic small polarons and ferromagnetic large polaron domains characterized by different values of the lattice distortions that are satisfactory compa red with those experimentally observed.