Two-dimensional charge order in layered 2-1-4 perovskite oxides

TL;DR

This study uses Monte Carlo simulations on a 3D Ising model with layered perovskite structure to explore charge ordering phenomena, revealing that interlayer frustration leads to 2D order with unique critical behavior.

Contribution

It demonstrates that interlayer frustration results in 2D long-range order and shows how monoclinic distortion induces 3D charge ordering, providing new insights into layered perovskite oxides.

Findings

Only 2D long-range order emerges due to interlayer frustration.

Critical exponents vary continuously with interlayer coupling.

Monoclinic distortion lifts degeneracy, inducing 3D charge order.

Abstract

Monte Carlo simulations are performed on the three-dimensional (3D) Ising model with the 2-1-4 layered perovskite structure as a minimal model for checkerboard charge ordering phenomena in layered perovskite oxides. Due to the interlayer frustration, only 2D long-range order emerges with a finite correlation length along the c axis. Critical exponents of the transition change continuously as a function of the interlayer coupling constant. The interlayer long-range Coulomb interaction decays exponentially and is negligible even between the second-neighbor layers. Instead, monoclinic distortion of a tetragonal unit cell lifts the macroscopic degeneracy to induce a 3D charge ordering. The dimensionality of the charge order in La$_{0.5}$Sr$_{1.5}$MnO$_4$ is discussed from this viewpoint.