Charge order and phase segregation in overdoped bilayer manganites

TL;DR

This paper models charge and orbital order in overdoped bilayer manganites near half doping, revealing how layered structure and interactions lead to complex magnetic and electronic phases.

Contribution

It introduces a model incorporating two $e_g$ orbitals and Coulomb repulsion to explain charge and orbital order in bilayer manganites.

Findings

Charge and orbital order are stabilized near half doping.

Layered magnetic structure is favored by reduced dimensionality.

Long-range interactions primarily drive charge order.

Abstract

There have been recent reports of charge ordering around $x=0.5$ in the bilayer manganites. At $x=0.5$, there appears to be a coexistence region of layered A-type antiferromagnetc and charge order. There are also reports of orbital order in this region without any Jahn-Teller effect. Based on physical grounds, this region is investigated from a model that incorporates the two $e_g$ orbitals at each Mn site and a near-neighbour Coulomb repulsion. It is shown that there indeed is both charge and orbital order close to the half-doped region coincident with a layered magnetic structure. Although the orbital order is known to drive the magnetic order, the layered magnetic structure is also favoured in this system by the lack of coherent transport across the planes and the reduced dimensionality of the lattice. The anisotropic hopping across the $e_g$ orbitals and the underlying layered structure largely determine the orbital arrangements in this region, while the charge order is primarily due to the long range interactions.