Structural modulation and electronic structural features in the charge ordered state ofLa0.5Sr1.5MnO4

Abstract

The structural changes associated with the charge ordering (CO) transition in layered ${\mathrm{La}}_{0.5}{\mathrm{Sr}}_{1.5}\mathrm{Mn}{\mathrm{O}}_{4}$ have been determined by electron diffraction using the multislice least-squares method. The results demonstrate that the structural deformations of the ${\mathrm{Mn}}^{3+}{\mathrm{O}}_{6}$ octahedra can be well characterized by a transverse modulation wave along the ⟨110⟩ direction. Based on these structural data, we have performed a theoretical calculation of the electronic structure by density functional theory plus the on-site Coulomb interaction $U$. The resultant density of states exhibits a clear band gap at the Fermi level for this low-temperature CO insulating state. It is also noted that the essential Jahn-Teller effects in this layered system can evidently affect the electronic structures and orbital hybridization appearing with the CO transition. Charge disproportionation and orbital ordering in ${\mathrm{La}}_{0.5}{\mathrm{Sr}}_{1.5}\mathrm{Mn}{\mathrm{O}}_{4}$ have been extensively discussed in comparison with the data obtained for the cubic perovskite ${\mathrm{La}}_{0.5}{\mathrm{Ca}}_{0.5}\mathrm{Mn}{\mathrm{O}}_{3}$.