Investigation of polarons in perovskite manganites

Perovskite manganites have aroused a great interest in their outstanding electrical and magnetic properties, but the characteristics of carriers in these materials are still under debate. According to the Mn-O chain, we build a one-dimensional tight-binding model to study the characteristics of charge carriers in manganites. It is obtained that at doping concentration x=0.5, the system shows a ferromagnetic state and the energy bands of spin up and spin down are completely splitted. A gap exists between valence band and conduction band, and all the electronic states are extended. With further doping, a localized electronic state appears, which we call a polaron. Accompanied with the electronic state, local distortions of the lattice and deep levels appear in the gap. The depth of the polaron increases with the doping quantity of electrons. It is also found that the polaron is spin polarized and has a maximum electronic charge of 0.621 e in the present parameters, beyond which the polaron will be divided into two separate states called solitons.