Charge ordering in half-doped manganites: Weak charge disproportion and leading mechanisms

The apparent contradiction between the recently observed weak charge disproportion and the traditional Mn3+/Mn4+ picture of the charge-orbital orders in half-doped manganites is resolved by a novel Wannier states analysis of the LDA+U electronic structure. Strong electron itinerancy in this charge-transfer system significantly delocalizes the occupied low-energy “Mn3+” Wannier states such that charge leaks into the “Mn4+”-sites. Furthermore, the leading mechanisms of the charge order are quantified via our first-principles derivation of the low-energy effective Hamiltonian. The electron-electron interaction is found to play a role as important as the electron-lattice interaction.