Spin and charge order in the CE phase ofLa1−xCaxMnO3

Abstract

The CE phase of ${\text{La}}_{1\ensuremath{-}x}{\text{Ca}}_{x}{\text{MnO}}_{3}$ is stable for $x\ensuremath{\gtrsim}0.5$ and displays long-range magnetic, charge, and orbital orders. The magnetic order of the Mn spins arises from the competition of the superexchange and double-exchange interactions and the checkerboard charge and the orbital order is the consequence of the Jahn-Teller coupling of the ${e}_{g}$ orbitals to the lattice. Using a mean-field slave-boson approach for the ${e}_{g}$ electrons in two orbitals per site with excluded multiple occupancy and Hund's rule coupling between the ${e}_{g}$ and ${t}_{2g}$ 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 ${e}_{g}$ bands in the Brillouin zone are grouped into two sets of 16 bands separated by a charge order gap. The phase diagram including the A, B, C, CE, and G phases reproduces the phase sequence observed in ${\text{La}}_{1\ensuremath{-}x}{\text{Ca}}_{x}{\text{MnO}}_{3}$.