Mean-field model for the CE-phase of manganites

Abstract

The CE phase of La0.5Ca0.5MnO3 displays long-range magnetic, charge and orbital order of the eg states of the Mn ions. The magnetic order of the t2g spins of Mn is determined by the antiferromagnetic superexchange and the ferromagnetic double-exchange. The checkerboard charge and the orbital order is the consequence of the Jahn-Teller coupling of the eg orbitals to the lattice. Using a mean-field slave-boson approach for the eg electrons in two orbitals per site with excluded multiple occupancy and Hund's rule coupling between the eg and t2g states, we obtain the tight-binding band structure of the CE phase. The unit cell of the CE phase consists of 16 sites. The 32 eg bands in the Brillouin zone are grouped into two sets of 16 bands separated by a charge order gap. The charge gap does not directly affect the properties of the compound. If long-range orbital order is included an additional gap opens at the Fermi level.